THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

DAVIS 


CALIKORXIA  STATE   NIINING  BUREAU. 

J.  J.  CRA'WFORD,  State  Mineralogist. 


BULLETIN    NO.   5. 


San  Francisco,  October,  1894. 


THE 


CYANIDE    PKOCESS 


ITS 


PRACTICAL  APPLICATION  AND  ECONOMICAL  RESULTS. 


By  dr.  a.  SCHEIDEL,  E.M. 


SACRAMENTO: 

STATE    OFFICE,       :       :       :      A.    J.    JOHNSTON,    SUPT.    STATE    PRINTING. 

1894. 
LIBRARY 

UNIVERSITY  or  CALIFORNIA 
DAVIS 


San  Fkancisco,  October  1,  1894. 

Hon.  J.  J.  Crawford,  State  Mineralogist,  San  Francisco,  Calif.: 

Dear  Sir:  In  accordance  with  your  letter  of  December  8,  1893,  I 
herewith  submit  my  report  on  the  cyanide  process.  I  have  endeavored 
to  describe  that  process  in  its  practical  application  and  economical 
results.  The  information  it  conveys  includes  my  own  experience,  and 
is  supplemented  from  articles  which  appeared  in  technical  periodicals; 
also  from  the  records  of  patents  granted  by  the  Patent  Offices  of  the 
United  States  and  Great  Britain,  and  from  the  Blue  Books  issued  by 
the  Mining  Departments  of  the  British  Colonies  of  Australasia.  I  am 
largely  indebted  for  special  communications  received  from  metallurgists 
in  charge  of  prominent  companies  and  important  works,  and  from  the 
officers  of  the  government  mining  departments  of  the  Australian  Colo- 
nies. It  has  seemed  advisable  with  some  "  improvements,"  and  generally 
with  the  patents,  to  simply  place  them  on  record  without  any  special 
comment. 

Respectfully  yours, 

A.  SCHEIDEL,  Ph.D.,  E.M. 


THE  CYANIDE  PROCESS 

ITS 

PRACTICAL  APPLICATION  AND  ECONOMICAL  RESULTS. 

By  A.  ScHEiDEL,  Ph.D.,  E.M. 


The  "cyanide  process"  for  extracting  gold  and  silver  from  ores  is 
based  on  the  fact  that  a  diluted  solution  of  potassium  cyanide  dissolves 
these  metals,  forming,  respectively,  auro-potassic  cyanide  and  argento- 
potassic  cyanide,  from  many  ores,  without  dissolving  to  any  material 
extent  the  other  components  thereof.  The  process  consists  of  treating 
suitable  ores,  when  finely  divided,  with  a  weak  solution  of  potassium 
cyanide,  either  by  allowing  the  solution  to  percolate  through  the  ore  or 
by  agitating  a  mixture  of  the  ore  and  solution.  This  part  of  the  opera- 
tion being  completed,  the  solution  is  separated  from  the  solid  material 
and  the  gold  and  silver  are  precipitated  in  metallic  form.  This  process 
for  the  extraction  of  gold  and  silver  is  comparatively  old  in  its  principle, 
but  modern  in  its  technical  application.  During  the  last  four  years  it 
has  been  introduced  into  almost  every  gold  field,  and  upwards  of 
$14,000,000  in  gold  and  silver  have  been  recovered  by  the  process,  which 
demonstrates  beyond  doubt  that  it  is  one  of  the  most  important  additions 
to  the  wet  methods  of  gold  and  silver  metallurgy.  The  aim  of  this 
paper  is  to  present  the  history  of  the  process  and  to  describe  the  ores  for 
which  it  is  adapted,  together  with  their  preparation  and  manipulation 
during  treatment.  The  economical  features  of  the  cyanide  process  are 
also  dwelt  on  at  some  length.  The  text  is  illustrated  by  plans  and 
diagrams. 

The  State  Mining  Bureau  of  California  was  among  the  first  in  the 
United  States  to  investigate  the  merits  of  the  cyanide  process,  as  set  forth 
in  a  paper  by  Dr.  W.  D.  Johnston,  in  the  Xth  Report  of  the  Bureau.  The 
process  has  since  found  extensive  application,  and  other  valuable  and 
interesting  papers  have  been  published,  but  an  exact  account  of  the 
methods  employed  in  all  parts  of  the  world  is  still  wanting.  This  writing 
is  undertaken  at  the  request  of  Hon.  J.  J.  Crawford,  State  Mineralogist  of 
California.  The  facts  herein  recorded  are  obtained  from  the  practical 
experience  of  the  writer  in  New  Zealand  and  the  United  States,  and  of 
others  who  have  been  very  successful  in  the  application  of  the  cyanide 
process.  I  take  great  pleasure  in  expressing  my  sincere  appreciation  of 
and  gratitude  for  the  assistance  my  contributors  have  extended.  I  desire 
especially  to  acknowledge  my  obligation  to  Mr.  John  S.  MacArthur,  of 
Glasgow,  Scotland,  and  to  Mr.  J.  M.  Buckland,  the  general  manager  of 
the  African  Gold  Recovery  Company,  Lim.,  in  Johannesburg,  South 
African  Republic.  In  order  to  allow  a  comparatively  full  description  of 
methods  and  appliances,  in  the  following  pages,  theoretical  matter  is 
limited  to  the  main  chemical  reactions  incidental  to  the* process,  and  an 
explanation  of  some  of  the  difficulties  most  frequently  met.  To  facili- 
tate the  consultation  of  the  paper,  I  prefix  the  following  synopsis: 


6  THE    CYANIDE    PROCESS. 

I.  History  of  process:  Solubility  of  gold  and  silver  in  cyanide  as 
known  to  Hagen,  Bagration,  Eisner,  Faraday;  its  technical 
application  by  Wright  and  Elkington;  its  metallurgical  appli- 
cation by  Rae,  Simpson,  Endlich  and  Miihlenberger,  Louis 
Janin,  Jr.,  Dixon,  MacArthur  and  Forrest,  Molloy,  A.  Janin  and 
Merrill,  W.  D.  Johnston. 
II.     Scope  of  process. 

III.  Chemistry  of  process. 

IV.  Demonstration  of  the  process.     Methods  of  operation: 

A.  The  agitation  process. 

B.  The  percolation  process. 

(o)  Percolation  of  ores. 

(6)  Percolation  of  tailings. 

(c )  Percolation  of  concentrates. 

C.  Cyanide  and  cyanide  solutions. 

D.  Treatment  of  the  gold  solutions.    Recovery  of  the  gold  and  silver. 

(a)  Precipitation  by  zinc. 

(b)  The  Molloy  process. 

(c)  The  Siemens  and  Halske  procesa. 

(d)  The  Pielsticker  process. 

(e)  The  Moldenhauer  process. 
(/)  The  Johnston  process. 

V.  Percentage  of  extraction. 

VI.  Working  costs  of  process. 

VII.  Cost  of  cyanide  plants. 

VIII.  Machinery  and  appliances. 

IX.  Laboratory  work. 

X.  Danger  in  working  the  process. 

XL  Exemplification  of  the  process.     The  process  in  various  countries: 

A.  Africa. 

B.  Australasia.  , 

(a)  New  Zealand. 
(&)  Tasmania. 

(c )  Western  Australia. 

(d)  South  Australia, 
(c)  Queensland. 

(/)  New  South  Wales. 
ig)  Victoria. 

C.  United  States  of  America. 

(a)  Utah. 
(6)  Montana. 

(c)  Colorado. 

(d)  Nevada. 

(e)  Arizona. 

If)  New  Mexico. 

\g)  South  Dakota.  ^ 

{h)  California. 

D.  Mexico,  Colombia,  Straits  Settlements,  Russia,  Borneo. 

XII.     Summary  and  conclusions. 
XIII.     Patents: 

Julio  IT.  Rae.    Improved  mode  of  treating  auriferous  and  argentiferous 
ores.    U.  S.  patent  61,866,  dated  February  5,  1S67. 

Thomas  C.  Clark.    Extracting  precious  metals  from  ores.    U.  S.  patent 
229,586,  dated  July  6,  1880. 

Hiram  W.  Faucett.    Process  of  treating  ore.    U.  S.  patent  236,424,  dated 
January  11,  1881. 

John  F.  Sanders.     Composition  for  dissolving  the  coating  of  gold  in  ore. 
U.  S.  patent  244,080,  dated  July  12,  1881. 

Jerome  W.  Simpson.    Process  of  extracting  gold,  silver,  and  copper  from 
their  ores.    U.  S.  patent  323,222,  dated  July  28,  1885. 
^         John  Stewart  MacArthur,  Robert  Wardrop   Forrest,   M.D.,  and   William 
Forrest,  M.B.    Improvements  in  obtaining  gold  and  silver  from  ores  and  other 
compounds.    English  patent  14,174;  1887. 


THE   CYANIDE    PROCESS.  • 

XIII.     Patents  (continued): 

John  Stewart  Mac  Arthur,  Robert  Wardrop  Forrest,  and  William  Forrest 
Process  of  obtaining  gold  and  silver  from  ores.  U.  S.  patent  403,202,  dated 
May  14,  1889. 

John  Stewart  MacArthur.  Metallurgical  filter.  U.  S.  patent  418,138,  dated 
December  24,  1889. 

John  Stewart  MacArthur,  Robert  Wardrop  Forrest,  and  William  Forrest. 
Process  of  separating  gold  and  silver  from  ores.  U.  S.  patent  418,137,  dated 
December  24,  1889. 

Edward  D.  Kendall.  Composition  of  matter  for  the  extraction  of  gold  and 
silver  from  ores.    U.  S.  patent,  dated  September  13,  1892. 

Bernard  Charles  Molloy.  Improvements  in  precipitating  and  collecting 
metals  from  solutions  containing  them.    English  patent  3,024;  1892. 

John  Cunninghame  Montgomerie.  Improvements  in  the  extraction  of 
gold  and  silver  from  ores  or  compounds  containing  the  same,  and  in  appa- 
ratus applicable  for  use  in  the  treatment  of  such  materials  by  means  of 
solvents.    English  patent  12,641;  1892. 

John  Stewart  MacArthur  and  Charles  James  Ellis.  Improvements  in  ex- 
tracting gold  and  silver  from  ores  and  the  like.  New  Zealand  paten t-speciti- 
cation,  June  29,  1893. 

Carl  Moldenhauer.  Improvements  in  recovering  gold  and  other  precious 
metals  from  their  ores.    ISIew  Zealand  patent-specihcation,  August  31,  1893. 

Carl  Pielsticker.  Improvements  in  the  extraction  of  gold  and  silver  from 
ores.    New  Zealand  patent-specification,  December  14,  1893. 

Alexis  Janin  and  Charles  W.  Merrill.  Process  of  leaching  ores  with  solu- 
tions of  alkaline  cyanides.    U.  S.  patent  515,148,  dated  February  20,  1894. 

William  David  Johnston.  Method  of  abstracting  gold  and  silver  from  their 
solutions  in  potassium  cyanides.    U.  S.  patent  522,260,  dated  July  3,  1894. 

XIV.     List  of  plans,  diagrams,  and  tables: 

Details  of  the  false  bottoms  of  the  percolation  vats.    (W.  R.  Feldtmann.) 
Plant  to  treat  a  minimum  of  2,000  tons  per  month.    (MacArthur.) 
'Table  giving  sizes  and  material  of  percolation  vats.    (A.  Scheidel.) 
Zinc  box.    (MacArthur.) 
Zinc  filter.    (A.  Scheidel.) 
Porcelain  filter.    (A.  B.  Paul.) 

Table  giving  extraction  results  on  various  ores.    (A.  Scheidel.) 
Discharging  tailings-vats    at  the   Langlaagte    Estate   Company's   plant. 

(W.  R.  Feldtmann.) 

Square  filter  vats  at  the  works  of  the  Crown  Company,  with  doors  for  the 

discharging  trucks.    (Irvine.) 
Variation  No.  1  in  designs  of  cyanide  plants.    (W.  R.  Feldtmann.) 
Variation  No.  2  in  designs  of  cyanide  plants.    (W.  R.  Feldtmann.) 
Variation  No.  3  in  designs  of  cyanide  plants.    (W.  R.  Feldtmann.) 
Side  discharge  at  percolation  vats.    (W.  R.  Feldtmann.) 
Bottom  discharge  at  percolation  vats.    (Chas.  Butters.) 
Bottom  discharge  at  percolation  vats.    (W.  E.  Irvine.) 
The  cyanide  works  of  the  Robinson  Company.    (Chas.  Butters.) 
The  cyanide  plant  of  the  Crown  Company.    (John  MacConnell.) 
The  Sylvia  Company's  Cyanide  Works,  Tararu,  Thames,  New  Zealand.    (A. 

Scheidel.) 

Melting  room  for  cyanide  bullion  in  the  Sylvia  Company's  Works,  Tararu, 

New  Zealand.    (A.  Scheidel.) 
The  tailings  cyanide  works  at  Waihi.    (A.  James.) 
The  concentrating  and  cyanide  extraction  works  of  the  Sylvia  Gold  and 

Silver  Mining  Company.    (A.  Scheidel.) 
The  cyanide  plant  of  the  Sylvia  Company  (plan  and  longitudinal  section). 

(A.  Scheidel.) 
Table  showing  the  concentrating  and  cyanide  process  in  the  works  of  the 

Sylvia  Company.    (A.  Scheidel.) 
Bullion  furnace.    (A.  Scheidel.) 

Wet-mill  cyanide  plant,  Revenue.    (F.  B.  &  R.  B.Turner.) 
Dry-mill  cyanide  plant.  Revenue.    (F.  B.  &  R.  B.  Turner.) 
U  tica  Company  cyanide  plant  (plan  and  longitudinal  section).  (A.  Scheidel.) 
The  vacuum  filter,  Utica  cyanide  plant.    (A.  Scheidel.) 
The  bullion  filter,  Utica  cyanide  plant.    (A.  Scheidel.) 
Agitator.    (J.  H.  Rac.) 
Metallurgical  filter.    (J.  S.  MacArthur.) 

Apparatus  for  treatment  of  ores,  etc.,  by  means  of  solvents.  (J.  C.  Mont- 
gomerie.) 

Improved  apparatus  for  the  extraction  of  gold  and  silver  from  ores.   (C.  M. 

Pielsticker.) 
Table  giving  analysis  of  gold  production  in  the  Witwatersrand  District  for 

April,  1894.    (Witwatersrand  Chamber  of  Mines.) 


;  THE   CYANIDE    PROCESS. 

XV.     List  of  abbreviations  of  literature: 

E.  &  M.  J. — Engineering  and  Mining  Journal,  New  York. 

M.  I. — Mineral  Industry. 

M.  S.  P. — Mining  and  Scientific  Press. 

Tr.  A.  I.  M.  E. — Transactions  of  the  American  Institute  of  Mining  Engineers. 

J.  S.  Chem.  I.— Journal  of  .Society  of  Chemical  Industry,  England. 

J.  fr.  Chem. — Journal  fiir  practische  Chemie. 

J.  Ch.  S. — Journal  Chemical  Society. 

Tr.  Phil.  Soc. — Transactions  of  the  Philosophical  Society. 

M.  Sc. — Moniteur  Scientifique. 

A.  Ch.  Ph.— Annales  de  Chimie  et  de  Physique. 
Ch.  N. — Chemical  News. 

B.  A.  I.  Sc. — Bulletin  de  I'Acad^mie  Imperiale  des  Sciences  de  St.  Peters- 
bourg. 

B.  S.  Ch. — Bulletin  de  la  Society  Chimique  de  Paris. 


HISTORY. 


I.    HISTORY. 


The  fact  of  gold  being  soluble  in  cyanide  of  potassium  solution  has 
been  known  for  a  considerable  time.  Hagen  is  reported  to  have  men- 
tioned it  in  1806.  Dr.  Wright,  of  Birmingham,  England,  used  gold- 
cyanide  solution  for  electroplating  in  1840j  he  made  this  application  in 
consequence  of  his  studies  of  Scheele's  report  on  the  solubility  of  gold- 
cyanide  in  a  cyanide  of  potassium  solution.  J.  R.  &  H.  Elkington 
patented  Wright's  invention;  they  speak  in  tbeir  patent-specification  of 
a  boiling  solution  of  gold  or  cyanide  of  gold  in  prussiate  of  potash. 
The  first  record  in  scientific  literature  of  experiments  in  which  metallic 
gold  was  dissolved  in  a  cyanide  of  potassium  solution  consists  in  Prince 
Pierre  Bagration's  paper  in  the  Bulletin  de  I'Academie  Imperiale  des 
Sciences  de  St.  Petersbourg,  1843,  t.  11,  p.  136.  Bagration,  who  alludes 
to  Elkington's  process,  preserved  cyanide  of  potassium  solution  in  a 
dish,  gilded  on  the  inside.  He  noticed  that  after  eight  days  the  whole 
gold  surface  had  been  attacked.  He  experimented  then  with  finely 
divided  gold  under  the  influence  of  the  galvanic  current;  the  latter  he 
soon  recognized  as  not  of  any  benefit  in  the  dissolving  process.  He  pre- 
cipitated the  gold  out  of  the  cyanide  solution  by  means  of  the  electric 
current  on  a  cathode  of  copper.  Continued  experiments  proved  the 
advantage  of  higher  temperature  during  the  dissolving  process,  and 
taught  the  precipitation  of  gold  from  its  still  warm  solution  by  means 
of  silver  or  copper  plates,  without  the  electric  current.  The  higher  tem- 
perature had,  however,  the  disadvantage  of  the  silver  and  copper  being 
strongly  attacked  by  the  cyanide  solution  during  the  precipitation  process. 
Bagration  extended  his  experiments  to  solutions  of  ferroeyanide,  which  he 
found  to  act  like  cyanide,  but  in  a  much  less  degree.  He  further  studied 
the  solubility  of  gold  in  the  form  of  plates,  in  cyanide,  and  found  it  to  be 
dissolved  in  such  form  at  a  considerable  rate  at  a  temperature  of  30°  to 
40°  C.  He  noticed  the  influence  of  the  air  on  the  reaction.  Bagration 
believes  that  hydrocyanic  acid  in  a  state  of  generation  is  a  gold  solvent, 
and  he  concludes  his  paper  with  the  remark  that  in  the  future,  cyanide 
of  potassium  must  be  enumerated  among  the  solvents  of  gold.  L.  Eisner 
published  in  J.  fr.  Chem.,  1844,  p.  441,  his  observations  on  the  reactions 
of  "reguline  metals"  in  an  aqueous  solution  of  cyanide.  He  found  that 
gold  and  silver  were  dissolved  in  potassium  cyanide  without  decomposi- 
tion of  water.  "The  dissolution  of  the  metals  is,  however,  the  conse- 
quence of  the  action  of  oxygen,  which,  absorbed  from  the  air,  decomposes 
part  of  the  cyanide."  His  reaction  has  been  expressed  by  others  in  the 
following  equation: 


2  Au  +  4  KCy  +  0  -f  H2O  = 

2  AuKCya  -f  2  KOH 

(Gold.)           (Cyanide    (Oxygen.)    (Water.) 
of  potassium.) 

(Auro-potassic            (Potassic 
cyanide.)                hydrate.) 

It  is  generally  called  Eisner's  equation.  Some  years  after,  Faraday 
made  use  of  the  solubility  of  gold  in  cyanide  solution  for  reducing  the 
thickness  of  gold  films  (Exp.  relations  of  gold  and  other  metals  to  light, 
Tr.  Phil.  Soc,  1857,  p.  147).  The  basis  of  the  most  modern  process 
for  the  extraction  of  gold  was  thus  provided.  It  took  many  years, 
however,  before  the  enumerated  facts* were  made  use  of  for  the  extrac- 
tion of  gold  from  ores.  In  1867,  Julio  H.  Rae  took  out  United  States 
patent  No.  61,866,  dated   February  5th,  for  an  "improved  method  of 


JO  THE   CYANIDE    PROCESS. 

treating  auriferous  and  argentiferous  ores  "  with  a  current  of  electricity 
in  connection  with  suitable  liquids — such,  for  instance,  as  cyanide  of 
potassium.  Rae's  process  is  an  agitation  process;  he  proposed  to  "  expose 
the  auriferous  or  argentiferous  rock  to  the  combined  action  of  a  current 
of  electricity  and  of  suitable  solvents,  and  to  separate  the  gold  or  silver 
from  the  rocks  containing  the  same  by  the  action  or  aid  of  electricity." 
The  principle  of  Rae's  process,  as  stated  by  him,  distinguishes  his 
method  from  the  modern  cyanide  process.  His  method  does  not  appear 
to  have  advanced  beyond  the  laboratory  stage  or  to  have  found  exten- 
sive and  successful  practical  application,  and  it  sank  into  oblivion. 
Since  then,  cyanide  of  potassium  in  connection  with  gold  and  silver 
metallurgy  has  repeatedly  been  made  a  patent  claim;  in  many  cases, 
however,  the  application  recommended  is  in  its  principle  different  from 
the  application  which  characterizes  the  modern  cyanide  process.  Thomas 
C.  Clark,  of  Oakland,  Cal.  (United  States  patent  No.  229,586,  July  6, 
1880),  roasted  his  ore  to  a  red  heat,  and  placed  it  in  that  condition  in  a 
cold  bath  composed  of  a  solution  of  salt,  prussiate  of  potash,  and  caustic 
soda.  H.  W.  Faucett,  of  St.  Louis,  Mo.  ( United  States  patent  No.  236,424, 
January  11, 1881),  subjects  hot  crushed  ores  to  the  action  of  disintegrat- 
ing chemicals,  cyanide  of  sodium  among  others,  in  solution  under 
pressure,  the  pressure  being  effected  by  the  steam  generated  by  the  con- 
tact of  the  hot  ores  with  the  chemical  solution  in  a  closed  vessel.  This 
treatment,  like  that  proposed  by  Clark,  was  intended  as  preliminary  to 
amalgamation.  John  F.  Sanders,  of  Ogden,  obtained  United  States 
patent  No.  244,080,  dated  July  12,  1881,  for  "composition  for  dissolving 
the  coating  of  gold  in  ore."  This  composition  is  made  of  cyanide  of 
potassium  and  glacial  phosphoric  acid.  He  stated  that  by  using  this 
mixture  he  could  dissolve  "  the  impure  coatings  of  gold,  leaving  the  gold 
free  and  exposed,  and  permitting  it  to  be  amalgamated."  It  is  evident, 
therefore,  that  these  processes  bear  no  similarity  or  relation  to  the 
modern  cyanide  process.  For  a  considerable  time,  cyanide  of  potassium 
has  been  used  in  the  gold  fields  of  California  and  Australasia  for  remov- 
ing film-coating  from  gold  in  ores;  its  application  in  the  pan-amalga- 
mation process  may  have  been  a  source  of  loss  of  gold. 

The  application  of  a  cyanide  of  potassium  solution  for  the  extraction 
of  gold  and  silver  direct  from  their  ores,  which  application  had 
been  neglected  since  Rae,  was  taken  up  again  by  Jerome  W. 
Simpson,  of  Newark,  N.  J.,  who  obtained  United  States  patent  No. 
323,222,  dated  July  28,  1885,  for  a  process  of  extracting  gold,  silver, 
and  copper  from  their  ores.  Simpson  reduced  his  ore  to  a  powder  and 
agitated  it  with  a  solution  of  certain  salts,  which  combine  chemically 
with  the  metal  in  the  ore  and  form  therewith  a  soluble  salt.  The 
salt  solution  was  composed  of  one  pound  of  cyanide  of  potassium,  one 
ounce  of  carbonate  of  ammonia,  one  half  ounce  of  chloride  of  sodium, 
and  sixteen  quarts  of  water.  This  solution  is  described  as  particularly 
adapted  to  ores  containing  gold,  silver,  and  copper  in  the  form  of  sul- 
phurets.  In  the  absence  of  silver  no  chloride  of  sodium  is  used;  for 
ores  rich  in  silver  a  proportionately  larger  quantity  of  chloride  of 
sodium  is  employed.  The  metals  dissolved  in  the  salt  solution  were 
precipitated  by  means  of  zinc,  suspended  therein  in  form  of  pieces  or 
plates.  Simpson  was  aware  that^  cyanide  of  potassium,  in  connection 
with  an  electric  current,  had  been  used  for  dissolving  metal,  and  also 
that  zinc  had  been  employed  as  a  precipitant.     What  he  claims  as  new 


HISTORY.  1 1 

is:  (1)  The  process  of  separating  gold  and  silver  from  their  ores,  which 
consists  in  subjecting  the  ore  to  the  action  of  the  solution  of  cyanide  of 
potassium  and  carbonate  of  ammonia,  and  subsequently  precipitating 
the  dissolved  metal  by  means  of  zinc.  (2)  The  process  of  separating 
metals  from  their  ores,  to  wit,  "subjecting  the  ore  to  the  action  of  a 
solution  of  cyanide  of  potassium,  carbonate  of  ammonia,  and  chloride  of 
sodium,  and  subsequently  precipitating  the  dissolved  metals." 

My  own  experiments  have  proved  that  the  addition  of  sodium  chlo- 
ride is  of  no  benefit  for  the  extraction  of  silver.  The  addition  of  ammonium 
carbonate  is  not  beneficial  to  the  extraction  of  either  gold  or  silver, 
except  under  certain  conditions,  when  it  may  be  substituted  advanta- 
geously by  an  alkali  or  an  alkaline  earth;  in  the  presence  of  base  metals 
it  is  of  disadvantage.  Simpson's  patent  description  appears  to  indi- 
cate that  he  had  not  discovered  the  most  important  property  of 
dilute  cyanide  solutions,  namely,  that  of  dissolving,  without  the  addi- 
tion of  other  chemicals,  the  noble  (in  preference  to  the  base)  metals. 
His  patent-claim  consists  eminently  in  adding  to  the  cyanide  solution 
the  chemicals  mentioned  above.  His  process,  like  that  of  Rae,  is  an 
agitation  process.  The  zinc  for  precipitating  the  bullion  he  used  in  the 
form  of  plates  or  pieces.  There  is  no  record  in  the  technical  literature 
in  reference  to  the  application  of  Simpson's  process  before  the  issue  of 
the  MacArthur  and  Forrest  patents  in  1889.  After  Rae  and  Simpson, 
others  have  made  experiments  with  cyanide  solutions  for  the  purpose  of 
gold  and  silver  extraction  from  ores.  F.  M.  Endlich  and  N.  H.  Miihlen- 
berger  are  reported  to  have  filed  a  caveat  in  1885,  without,  however, 
securing  a  patent,  the  former  having  apparently  become  doubtful  as  to 
the  applicability  of  cyanide  as  an  economical  process  (E.  &  M.  J., 
1891,  p.  86).  Louis  Janin,  Jr.,  made  interesting  experiments  in  the 
same  direction  in  Park  City,  Utah,  of  which  he  published  the  results 
in  1888  (E.  &  M.  J.,  1888,  p.  548).  These  experiments  refer  chiefly 
to  silver  extraction,  but  he  mentions  as  well  the  results  on  gold  ores; 
his  results  appear  to  have  been  encouraging,  and  led  to  his  filing  a  caveat 
on  May  1, 1886,  but  this  was  not  pushed  on  to  the  taking  out  of  a  patent. 

In  the  southern  hemisphere,  W.  A.  Dixon  has  made  experiments  with 
cyanide  on  Australian  ores  as  early  as  1887.  He  recorded  his  results, 
which  are  at  least  of  historical  interest,  in  a  paper  read  before  the  Royal 
Society  of  New  South  Wales.  Dixon  describes  therein  the  experiments 
made  by  him  at  the  instigation  of  the  Government  Inspector  of  Mines, 
who  suggested  that  the  extraction  of  gold  from  complex  minerals  was  a 
subject  worthy  of  investigation.  Dixon  tried  on  such  ores  amalgama- 
tion and  a  number  of  solvents.  He  found  "the  aurocyanides  of  the 
alkaline  metals  of  sufficient  stability  to  render  their  use  possible  for  the 
extraction  of  the  gold."  He  mentions  Bagration's  and  Eisner's  publi- 
cations and  alludes  to  Rae's  patent,  of  which,  however,  he  possessed  no 
particulars.  Dixon  feared  that  "the  high  price  of  cyanide,  its  insta- 
bility when  exposed  to  the  air,  and  its  extremely  poisonous  qualities," 
would  prove  such  obstacles  as  to  preclude  its  use  for  metallurgical  pur- 
poses. He  found  the  reaction  between  gold  and  cyanide  slow  if  "  the 
gold  was  at  all  dense";  in  presence  of  alkaline  oxidizing  agents,  how- 
ever, he  found  the  dissolving  process  suflliciently  rapid.  Dixon  experi- 
mented also  with  the  ferrocyanide  of  potassium.  His  results  generally, 
did  not,  as  far  as  known,  lead  to  the  metallurgical  application  of 
cyanide  as  a  gold  and  silver  solvent. 


12  THE    CYANIDE    PROCESS. 

T  have  thus  described  the  history  of  cyanide  of  potassium  .as  a  gold 
dissolving  agent  from  the  early  laboratory  experiments  up  to  its  metal- 
lurgical application  for  ore  extraction;  this  latter,  however,  did  not  gain 
any  practical  importance  until  John  S.  MacArthur  and  W.  Forrest,  of 
Glasgow,  Scotland,  took  out  their  patents  for  the  use  of  cyanide  as  a 
gold  and  silver  solvent  from  ores,  and  gave  thereby  the  cyanide  process 
a  start  all  over  the  world.  Their  patents  mark  an  epoch  in  gold 
metallurgy.  The  results  of  the  application  of  cyanide,  as  suggested  by 
them,  have  been  very  satisfactory;  the  $14,000,000  of  bullion  pro- 
duced by  it  during  the  five  short  years  of  its  working  represents  what, 
by  the  ordinary  methods,  would  have  been  irrecoverably  lost;  hence  its 
value  and  importance  from  the  standpoint  of  metallurgy  and  political 
economy.  The  experiments  of  MacArthur  and  Forrest  with  gold  dissolv- 
ing reagents  occupied  some  years  before  their  English  cyanide  patents 
were  applied  for  (J.  S.  MacArthur,  J.  S.  Chem.  I.,  March  31,  1890,  No.  3, 
vol.  9).  They  drew  out  a  list  of  possible  solvents  having  a  stronger 
affinity  for  gold  than  for  sulphides,  which  included  the  cyanides,  and 
which  they  found  to  solve  the  problem.  Their  experiments,  conducted 
first  on  a  small  scale  and  with  ores  of  many  kinds  and  of  different 
sources,  were  so  satisfactory  that  they  gradually  worked  on  a  larger  scale, 
and  their  results  formed  the  basis  for  the  introduction  of  the  cyanide 
process  into  most  gold-producing  fields.  Their  English  patent  was 
applied  for  October  19,  1887.  Since  then  they  applied  for  and  obtained 
patents  in  many  gold-producing  countries.  Their  United  States  patents 
are  dated  as  follows:  403,202,  May  14, 1889;  418,137,  December  24, 1889; 
418,138,  December  24,  1889.  Their  invention  is  described  "as  having 
principally  for  its  object  the  obtaining  of  gold  from  ores,  but  it  is  also 
applicable  for  obtaining  silver  from  ores  containing  it  whether  with  or 
without  gold,  and  it  comprises  an  improved  process,  which,  while  appli- 
cable to  auriferous  and  argentiferous  ores  generally,  is  advantageously 
and  economically  effective  with  refractory  ores,  or  ores  from  which  gold 
and  silver  have  not  been  satisfactorily  or  profitably  obtainable  by  the 
amalgamating  or  other  processes  hitherto  employed;  such  as  ores  con- 
taining sulphides,  arsenides,  tellurides,  and  compounds  of  base  metals 
generally,  and  ores  from  which  the  gold  has  not  been  easily  or  completely 
separable  on  account  of  its  existing  in  the  ores  in  a  state  of  extremely 
j&ne  division."  The  patentees  describe  their  invention  (I  am  following 
United  States  patent  403,202)  as  consisting  in  subjecting  the  ores  to  the 
action  of  a  solution  containing  a  small  quantity  of  cyanide,  without  any 
other  chemically  active  agent.  In  dealing  with  ores  containing  per  ton 
twenty  ounces  or  less  of  gold  or  silver,  or  gold  and  silver,  they  find  it 
most  advantageous  to  use  a  quantity  of  cyanide,  the  cyanogen  of  which 
is  equal  in  weight  to  from  one  to  four  parts  for  every  thousand  parts  of 
the  ore  dissolved  in  a  quantity  of  water  of  about  half  the  weight  of  the  ore ; 
they  generally  use  a  solution  containing  two  parts  of  cyanogen  for  every 
thousand  parts  of  the  ore.  In  the  case  of  richer  ores,  while  increasing  the 
quantity  of  cyanide  to  suit  the  greater  quantity  of  gold  or  silver,  they  also 
increase  the  quantity  of  water  so  as  to  keep  the  solution  dilute;  in  other 
words,  the  cyanide  solution  should  contain  from  two  to  eight  parts,  by 
weight,  of  cyanogen  to  one  thousand  parts  of  water,  and  the  quantity 
of  the  solution  used  should  be  determined  by  the  richness  of  the  ore. 
The  patentees  state:  "By  treating  the  ores  with  the  dilute  and  simple 
solution  of  a  cyanide,  the  gold  or  silver  is,  or  the  gold  and  silver  are, 


HISTORY.  13 

obtained  in  solution,  while  ahy  base  metals  in  the  ores  are  left  undis- 
solved except  to  a  practically  inappreciable  extent;  -whereas,  when  the 
cyanide  is  used  in  combination  with  an  electric  current,  or  in  conjunc- 
tion with  another  chemically  active  agent,  such  as  carbonate  of  ammo- 
nia, or  chloride  of  sodium,  or  phosphoric  acid,  or  when  the  solution 
contains  too  much  cyanide,  not  only  is  there  a  greater  expenditure  of 
chemicals  in  the  first  instance,  but  the  base  metals  are  dissolved  to  a 
large  extent  along  with  the  gold  or  silver,  and  their  subsequent  separation 
involves  extra  expense,  which  is  saved  by  their  process."  Later  on 
MacArthur  and  Forrest  obtained  patents  covering  the  use  of  zinc  in  a 
fine  state  of  division  for  the  purpose  of  precipitating  gold  and  silver 
from  cyanide,  chloride,  bromide,  thiosulphide,  sulphate,  or  other  similar 
solutions;  they  further  protected  the  use  of  an  alkali  or  alkaline  earth 
for  neutralizing  ores  preparatory  to  subjecting  the  same  to  the  action  of 
cyanogen  or  of  a  C3'anide.  The  MacArthur-Forrest  patent-claims  con- 
sist, therefore,  in  three  points:  (1)  The  application  of  diluted  solutions 
of  cyanide  (not  exceeding  eight  parts  of  cyanogen  to  one  thousand  parts 
of  water);  (2)  the  use  of  zinc  in  a  fine  state  of  division;  (3)  the  pre- 
paratory treatment  of  the  ore,  which  has  become  partially  oxidized  by 
exposure  to  the  weather,  with  an  alkali  or  alkaline  earth,  for  the  purpose 
of  neutralizing  the  salts  of  iron  or  other  objectionable  ingredients  formed 
by  partial  oxidation. 

It  is  not  the  purpose  of  this  paper,  which  is  intended  to  describe  the 
historical  development  of  the  cyanide  process  and  its  present  forms  of 
application,  to  enter  into  a  judicial  discussion  of  patent-claims  and 
patent-rights.  It  is  the  duty  of  the  historian  to  date  the  cyanide 
process  as  a  commercial  success  from  1890,  when  it  was  introduced  as 
"the  MacArthur-Forrest  process"  on  the  Witwatersrand  gold  fields,  in 
the  South  African  Republic.  Its  success  as  a  metallurgical  experiment 
may  be  dated  from  the  tests  made  on  a  large  scale  with  ore  from  the  New 
Zealand  Crown  Mine  in  June  and  July,  1888.  The  practicability  of 
the  cyanide  process  once  established,  others  endeavored  to  introduce 
improvements  in  its  application,  which  they  protected  by  letters  patent. 
A  patent  which  once  promised  to  become  of  practical  importance  is  that 
of  B.  C.  MoUoy,  of  Johannesburg,  whose  "improvement"  consists  in  the 
abolition  of  zinc  as  a  precipitant  of  gold,  and  in  the  revivification  of  the 
cyanide  of  potassium  in  the  solution.  In  this  process  the  ore  is  treated 
with  cyanide  of  potassium  as  usual;  the  resulting  liquors  are  passed 
through  a  "patent  Molloy  separator,"  which  consists  of  an  amalgama- 
tor, the  mercury  of  which  is  constantly  being  charged  electrolytically 
with  potassium.  The  potassium  on  coming  into  contact  with  the  water 
of  the  solution  decomposes  it  with  the  evolution  of  hydrogen  and  the 
formation  of  the  oxide  of  the  alkaline  metal.  The  nascent  hydrogen 
decomposes  the  solution  of  the  cyanide  of  gold,  and  sets  the  gold  free, 
which  is  precipitated  upon  and  collected  by  the  mercury;  the  metal  of 
the  alkaline  oxide  reacts  upon  the  cyanogen  compound,  and  so  repro- 
duces the  cyanide  of  potassium.  The  original  solution,  thus  regenerated, 
is  then  ready  for  use  again.  (In  reference  to  further  details  see  under 
precipitation  of  gold  and  silver,  p.  38.) 

Among  other  cyanide  patent-specifications  may  be  mentioned  the  fol- 
lowing: John  C.  Montgomerie,  of  Scotland,  obtained  English  patent  No. 
12,641,1892,  "for  improvements  in  the  extraction  of  gold  and  silver 
from  ores  and  in  apparatus  applicable  for  use  in  the  treatment  of  such 


14  THE    CYANIDE    PROCESS. 

by  means  of  solvents."  His  process  is  the  well-known  agitation  process 
of  finely  divided  ore  with  cyanide  solution  and  the  addition  of  an  alka- 
line oxide  "  for  the  purpose  of  economizing  the  solvent  and  expediting 
its  action."  The  patent-specification  does  not  contain  any  claims  which 
might  be  termed  either  an  invention  or  an  improvement,  either  chemic- 
ally or  mechanically.  One  of  the  latest  additions  to  the  cyanide  patent 
literature  is  United  States  patent  515,148,  dated  February  20,  1894,  of 
Alexis  Janin  and  Charles  W.  Merrill,  for  a  process  of  leaching  ores  with 
solutions  of  alkaline  cyanides.  (For  patent-specification,  see  Appendix.) 
They  claim  as  new  "  the  art  of  leaching  ores  with  solution  of  alkaline 
cyanides,  which  consists  in  first  leaching  the-  ore  with  such  solutions, 
then  adding  to  the  solution  an  agent  which  will  precipitate  the  silver 
present  as  a  sulphide,  and  then  precipitating  the  gold  in  the  solution 
with  metallic  zinc."  The  practical  advantages  of  this  complication  will 
have  to  be  proved. 

A  patent  description  of  interest,  although  not  a  "  cyanide  process " 
strictly  speaking,  is  that  of  E.  D.  Kendall,  of  Brooklyn,  N.  Y.,  dated 
September  13,  1892,  who  claims  the  use  of  potassium  ferrocyanide  com- 
bined with  cyanide  of  potassium,  for  extracting  gold  and  silver  from 
ores, etc.,  as  his  invention.     (For  patent-specification,  see  Appendix.) 

A  further  addition  to  the  patent  literature  is  the  specification  of  Mac- 
Arthur  and  Ellis,  who  propose  to  increase  the  efficiency  and  economy  of 
the  process  in  cases  in  which  from  the  nature  of  the  ores  treated  or  other 
circumstances,  soluble  sulphides  are  formed,  which  retard  and  objec- 
tionally  affect  the  action  of  the  cyanide  on  the  precious  metals  by  adding 
to  the  ore  or  the  cyanide  solution  suitable  salts  or  compounds  of  metals 
which  will  form  with  the  sulphur  of  the  soluble  sulphides  an  insoluble 
or  inert  sulphide.  For  this  purpose  preference  is  being  given  to  the 
metallic  salts  or  compounds  in  the  following  order:  Salts  or  compounds 
of  lead — such  as  plumbates.  carbonates,  acetate  or  sulphate  of  lead — 
sulphate  or  chloride  of  manganese,  zincates,  oxides,  or  chloride  of 
mercury,  ferric  hydrate  or  oxide.  The  proportion  to  Idc  used  is  easily 
to  be  ascertained  by  trials  of  a  few  samples  in  each  case.  (See  patent- 
specification  of  John  Stewart  MacArthur  and  Charles  T.  Ellis,  in  Ap- 
pendix.) 

C.  Moldenhauer  proposes  to  render  the  cyanide  process  more  expedi- 
tious and  considerably  cheaper  by,  firstly,  adding  to  the  cyanide  solution 
an  artificial  oxidizing  agent,  by  preference  ferricyanide  of  potassium  in 
alkaline  solution,  and,  secondly,  in  precipitating  the  extracted  precious 
metal  out  of  its  cyanide  solution  by  means  of  aluminium,  or  alloys,  or 
amalgam  thereof.     (See  patent-specification  in  Appendix.) 

C.  M.  Pielsticker  reverts  to  the  application  of  the  electric  current,  in 
conjunction  with  the  cyanide  solution.  He  proposes  to  continuously 
circulate  the  solvent,  to  continuously  precipitate  the  dissolved  precious 
metals  by  electrolysis,  and  continuously  regenerate  thereby  the  reagent. 
(See  patent  specification  in  Appendix.) 

The  latest  patent  in  connection  with  cyanide  treatment  of  ores  is  that 
of  Dr.  W.  D.  Johnston,  "for  abstracting  gold  and  silver  from  their 
cyanide  solutions  by  means  of  pulverized  carbon"  (for  further  details, 
see  page  40). 

To  make  this  report  as  complete  as  circumstances  permit,  I  append 
the  specifications  of  the  patents  which  have  been  mentioned  in  the  body 


SCOPE   OP    PROCESS.  15 

of  this  paper,  that  the  mining  public  may  know  the  exact  wording  of 
descriptions  and  claims. 

Such  is  the  history  of  the  cyanide  process,  rapidly  sketched  by  tracing 
its  development  through  the  phases  of  its  evolution  and  the  intricacies 
of  its  patent  literature.  The  modern  cyanide  process  consists  in  the 
treatment  of  ores  by  means  of  dilute  cyanide  of  potassium  solutions,  as 
a  rule  without  the  addition  of  other  chemical  substances,  and  in  the 
subsequent  precipitation  of  the  gold  and  silver  from  the  solution  by 
means  of  zinc  in  form  of  shavings.  It  is  commonly  known  as  the  Mac- 
Arthur- Forrest  process.  I  now  propose  to  enter  into  a  description  of  the 
process  itself.  I  embody  in  it  the  information  given  me  by  Mr.  John  S. 
MacArthur,  of  Glasgow,  Scotland. 


II.     SCOPE  OF  PROCESS. 

The  process  can  be  advantageously  applied  to  many  gold  ores  and 
many  silver  ores,  and  is  often  suitable  for  ores  which  are  generally  con- 
sidered as  rebellious  or  refractory.  The  word  "  ore ''  is  here  meant  to 
include  ores,  tailings,  concentrates,  ajid  all  similar  products  from  ore. 
The  term  "refractory"  is  used  to  signify  any  ore  which  cannot  be  satis- 
factorily amalgamated.  The  refractory  character  of  such  ores  can  be 
caused  by  the  presence  of  base  metals  in  combination  with  sulphur  or 
arsenic,  or  otherwise  by  their  physical  structure,  which  prevents  the  gold 
from  coming  in  contact  with  the  mercury  during  the  amalgamation 
process.  To  the  latter  class  belong  the  ores  in  which  the  gold  is  "coated" 
with  substances  which  prevent  metallic  contact  ("rusty  gold").  (An 
excellent  instance  of  such  coated  ore  is  that  found  in  the  Mount  Morgan 
Mine,  in  Queensland,  where  the  finely  divided  gold  is  coated  with  a  film 
of  what  has  been  termed  hydrous  peroxide  of  iron,  which  makes  the 
gold  absolutely  refractory  to  amalgamation.)  To  the  same  class  of 
refractory  ores  belong  those  in  which  the  gold  is  so  finely  divided  that 
the  film  of  air  surrounding  the  auriferous  particles  prevents  amalgama- 
tion even  under  the  most  favorable  conditions.  The  base  metals  which 
most  frequently  accompany  refractory  ores  are  iron,  zinc,  lead,  copper, 
and  antimony — usually  as  sulphides,  sometimes  as  arsenides.  When 
ores  containing  gold,  silver,  copper,  zinc,  iron,  etc.,  are  treated  with  solu- 
tions of  cyanide  of  potassium,  these  metals  are  dissolved  more  or  less, 
forming  soluble  cyanides.  The  solvent  action  on  the  base  metals  can 
be  reduced  to  a  minimum  by  reducing  the  strength  of  the  solutions,  the 
readily  soluble  gold  and  silver  being  easily  dissolved  out  with  only  traces 
of  copper,  zinc,  etc.  The  action  of  these  weak  cyanide  solutions  on  iron, 
lead,  arsenic,  etc.,  is  practically  nil,  and  the  solvent  action  on  copper  or 
zinc  depends  much  upon  the  state  of  chemical  combination  in  which 
they  exist. 

The  cyanide  process  is  adapted  to  treat  most  of  such  refractory  ores 
as  are  described  above.  The  principal  exce])tions  are  the  ores  which 
contain  hydrated  copper  oxides  and  copper  carbonates,  and  thdse  which 
contain  an  appreciable  quantity  of  antimony.  "When  copper  com- 
pounds exist  in  a  state  physically  hard,  the  cyanide  solution  does  not 
readily  act  on  them;  but  when  the  copper  compounds  are  soft,  porous, 
and  spongy,  the  action  of  the  cyanide  is  so  decided  as  to  interfere  mate- 
rially with  its  action  on  gold"  (MacArthur).     In  reference  to  copper 


16  THE    CYANIDE    PROCESS. 

sulphide  I  found  it  no  impediment  to  the  process;  carbonate  of  copper, 
however,  was  so  readily  attacked  by  cyanide  that  its  presence  proved 
absolutely  prohibitive  to  the  extraction  of  silver  and  interfered  seri- 
ously with  the  extraction  of  gold.  This  most  refractory  ore,  that  I  am 
speaking  of,  came  from  old  workings  in  the  Sylvia  Mine,  Tararu,  New 
Zealand,  where  part  of  the  ledge  containing  a  large  percentage  of  copper 
pyrites  had  been  exposed  for  many  years  to  the  influence  of  moisture 
and  the  atmosphere;  the  resulting  carbonate  was  hard,  but  notwith- 
standing this  its  reaction  on  cyanide  solutions  w^as  very  marked.  One 
and  a  fourth  ounce  of  such  copper  ore,  finely  divided  and  shaken  for  less 
than  fifteen  minutes  with  a  2.73  per  cent  cyanide  of  potassium  solution, 
reduced  the  strength  of  the  solution  to  0.05  per  cent  of  cyanide.  The 
treatment  of  the  ore  in  question  proved  that  the  affinity  of  cyanide  to 
gold  is  at  least  equal  to  that  of  cyanide  to  copper,  and  very  much  greater 
than  to  silver,  as,  notwithstanding  the  rapid  consumption  of  cyanide 
by  the  copper  compound,  upwards  of  70  per  cent  of  the  gold  assay- 
value  was  extracted  by  cyanide  solution  of  the  usual  strength,  whereas 
at  the  same  time  absolutely  no  silver  had  gone  into  solution.  A  pre- 
liminary treatment  of  such  ore  by  sulphuric  acid  had  a  beneficial  eftect 
on  the  consumption  of  cyanide  and  thereby  on  the  extraction  of  silver. 
"In  the  case  of  antimonial  ores,  there  is  little  or  no  interaction 
between  the  antimony  and  the  cyanide,  consequently  the  latter  is  not 
taken  up;  but  as  gold  seems  to  be  very  firmly  held  by  antimony,  and 
as  the  compound  is  very  impervious,  the  cyanide  is  unable  to  penetrate 
the  mass,  and  to  dissolve  and  separate  the  precious  from  the  base  metals. 
In  the  case  of  both  copper  and  antimon}'  the  cyanide  solution  will  act, 
but  in  the  case  of  copper,  if  there  is  much  present  and  acted  upon,  the 
consumption  of  cyanide  is  so  great  that  the  operation  is  not  profitable, 
and  in  the  case  of  the  antimonial  ores,  though  the  cyanide  will  act  with 
fine  grinding  and  long  contact,  the  expense  involved  often  overbalances 
the  value  of  the  gold  contents"  (MacArthur).  The  physical  state  in 
which  obnoxious  compounds  are  found,  is  of  the  greatest  importance. 
Hard-surfaced  crystals  are,  even  if  finely  divided,  naturally  less  acted 
upon  by  cyanide  than  soft,  spongy  masses  of  the  same  size.  For  tech- 
nical purposes,  cyanide  treatment  of  any  ore  will  be  called  unsuccessful 
if  the  large  consumption  of  cyanide  precludes  a  commercial  success, 
although  finally  a  satisfactory  extraction  in  percentage  may  be  achieved. 


ni.    THE  CHEMISTRY   OF   THE   PROCESS. 

The  chemical  reaction  on  which  the  cyanide  process  of  gold  extraction 
rests  is  that  of  the  formation  of  the  double  cyanide  of  gold  and  potassium: 

2  Au  -f  4  KCy  +  0  +  HgO  =  2  AuKCyj  -f  2  KOH 

(Gold.)  (Cyanide     (Oxygen.)    fWater.)         (Auro-potassic  (Potassic 

of  potassium.)  cyanide.)  hydrate.) 

That  of  silver  extraction  produces  the   double  cyanide  of  silver  and 
potassium: 

2Ag   -I-    4  KCy    -f    0    +    H2O   =   2  AgKCys   +    2  KOH 

/Silver.)  (Cyanide  of    (Oxygen.)     (Water.)         (Argento-potassic  (Potassic 

potassium.)  cyanide)  hydrate.) 


THE    CHEMISTRY    OF    THE    PROCESS.  17 

Silver  in  the  metallic  state  is,  however,  rarely  met  with  in  ores  which 
are  subjected  to  cyanide  treatment.  The  part  taken  by  oxygen  in  these 
reactions,  first  noticed  by  Prince  Bagration  and  later  confirmed  by 
Eisner,  has  of  late  been  disputed,  but  again  confirmed  by  McLaurin, 
who  published  his  experiments  (J.  Ch.  S.,  1893,  May,  p.  724)  in  refer- 
ence to  the  question,  and  came  to  the  following  conclusions:  (1)  That 
oxygen  is  necessary  for  the  solution  of  gold  in  cyanide  of  potassium,  and 
that  it  combines  with  the  potassium  of  the  potassium  cyanide  in  the 
proportions  required  by  Eisner's  equation;  (2)  That  the  rate  of  solu- 
tion of  gold  in  a  solution  of  potassium  cyanide  passes  through  a  maxi- 
mum in  passing  from  dilute  to  concentrated  solution,  and  this  remark- 
able variation  is  capable  of  explanation  by  the  fact  that  the  solubility 
of  oxygen  in  a  cyanide  solution  decreases  with  the  concentration.  The 
double  compounds  of  cyanide  of  potassium  and  gold  and  silver,  respect- 
ively, have  been  described  in  the  Annales  de  Chimie  et  de  Physique,  53, 
p.  462,  1858,  and  in  Bull,  de  la  Societe  Chimique  de  Paris,  29,  1878,  p. 
460.     Both  compounds  are  easily  soluble  in  water. 

The  cyanide  process,  as  illustrated  by  the  before-mentioned  equations, 
appears  very  simple  indeed.  Its  adoption  in  many  places  has  been  very 
rapid,  and  its  success,  particularly  on  the  tailings  of  the  Johannesburg 
mills,  has  been  great.  The  practical  working  and  technically  success- 
ful carrying  out  of  cyanide  treatment  of  any  ore,  even  under  the  most 
favorable  circumstances,  is  beset  with  complications,  which  require  a 
■careful  study  of  all  the  circumstances  connected  with  the  case.  All 
operations  offer  occasions  for  loss  and  opportunities  for  improvement. 
The  reaction  between  cyanide  and  the  metals,  so  simple  in  theory,  is  in 
practice  more  or  less  complicated  by  the  reaction  of  other  ore  com- 
pounds on  the  cyanide  and  by  other  causes  which  it  will  be  useful  to 
investigate.  That  such  reactions  take  place  is  put  in  strong  evidence  by 
the  amount  of  cyanide  consumed  in  treating  ores,  which  is  always  con- 
siderably larger  than  the  quantity  theoretically  necessary  to  dissolve 
the  gold.  In  accordance  with  Eisner's  equation,  10  parts  of  cyanide 
should  dissolve  15.12  parts  of  gold.  In  the  works  at  Johannesburg, 
however,  in  treating  free-milling  ore,  40  parts  of  cyanide  are  required  to 
dissolve  one  part  of  gold;  that  is  to  say,  40  parts  of  cyanide  are  con- 
sumed for  each  part  of  gold  obtained.  The  main  reason  for  this  fact 
must  be  looked  for  in  secondary  reactions,  which  as  yet  have  only  been 
partly  studied.  The  great  loss  of  cyanide  takes  place  during  the 
extraction  process,  and  particularly  during  the  first  part  of  it,  as  proved 
by  the  rapid  diminution  in  the  strength  of  the  solution.  The  loss  of 
cyanide  in  the  zinc  boxes  has  often  been  exaggerated  (see  page  34). 
A  loss  of  cyanide  occurs  by  absorption  in  vats  and  tanks,  which  is 
given  as  high  as  one  pound  per  ton  of  ore  in  Johannesburg  (Butters 
and  Clennell).  Some  loss  will  always  result  from  the  action  of  carbonic 
acid  gas,  which  is  always  present  in  the  atmosphere,  and  displaces 
cyanogen  from  the  alkali,  setting  prussic  acid  free,  which  escapes  into 
the  air;  if  caustic  alkali  is  present  the  freed  prussic  acid  will  be  neu- 
tralized. The  extent  of  loss  by  hydrolysis  requires  further  investiga- 
tion. The  presence  of  free  sulphuric  acid  or  other  products  of  more 
or  less  advanced  decomposition  of  pyritic  matter  will  naturally  consid- 
erably interfere  with  the  simple  reaction  by  increasing  the  consumption 
of  cyanide,  and  may,  under  the  most  unfavorable  circumstances,  com- 
pletely prevent  successful  treatment.  "  In  many  cases  tailings  which 
2cp 


18  THE   CYANIDE    PROCESS. 

have  been  exposed  to  the  weather  contain  oxidized  compounds,  such  as 
sulphate  of  iron,  and  similar  sulphates  of  alumina  and  magnesia, 
formed  by  the  action  of  the  metallic  sulphates  on  the  earthy  constitu- 
ents of  the  ore."  When  this  is  the  case  it  is  advisable  to  give  such  tail- 
ings one  or  more  preliminary  water-washings,  because  the  cyanide  is 
partly  absorbed  and  partly  decomposed  by  these  substances,  as  seen  in 
the  following  equations: 

FeSO^  +  2  KCy  =  FeCys  +  K2SO4 
FeaSCSO^)  +  6  KCy  +  3  HgO  =  FcaOg  -f  3(K2S04)  -f  6  HCy  ' 

From  these  equations  it  will  be  seen  that  the  ferrous  oxide  combines 
with  cyanogen,  and  that  the  sulphuric  acid,  forming  the  second  con- 
stituent of  the  ferric  salt,  liberates  hydrocyanic  acid,  which  being  vola- 
tile is  not  available,  and  moreover  constitutes  a  loss  and  a  danger.  The 
action  of  the  sulphates  of  alumina  and  magnesia  has  not  been  generally 
and  sufficiently  recognized.  These  salts  act  practically  as  if  they  were 
sulphuric  acid:  hydrocyanic  acid  is  liberated  and  alumina  or  magnesia, 
as  the  case  may  be,  precipitated,  as  shown  in  the  following  equations: 

Al23(S04)  +  6  KCy  -f-  3  H2O  =  AI2O3  -{-  3  (K2SO4)  -f  6  HCy 
MgSO^  +  2  KCy  +  H2O  =  MgO  -f  K2SO4  +  2  HCy 

The  remedy  for  these  troubles  is,  as  before  stated,  water-washing,  in 
some  cases  followed  by  a  lime  or  soda  treatment.  Reference  only  has 
been  made  to  ferrous  sulphate  as  a  soluble  salt,  but  it  has  been  found 
that  the  basic  ferrous  salts,  which  exist  to  a  greater  or  less  extent  in 
"weathered"  tailings,  are  insoluble  in  water,  and  yet  act  detrimentally 
on  cyanide.  In  any  case  it  is  difficult  to  wash  out  the  last  traces  of 
any  soluble  substance,  and  it  is  wise  to  economize  cyanide  by  an  alkaline 
treatment.  "While  ferrous  salts,  soluble  or  insoluble,  exist  in  the 
tailings,  the  lime  or  soda  combines  with  the  acid  and  deposits  the 
ferrous  oxide  or  hydrate  in  the  tailings.  The  ferrous  oxide  would  still 
absorb  cyanogen  if  a  cyanide  solution  were  present,  but  if  the  air  has 
free  access  before  a  cyanide  solution  is  applied,  the  ferrous  oxide  is 
oxidized  to  ferric  oxide,  which  does  not  combine  directly  with  cyanogen. 
It  will  thus  be  seen  that  where  salts  of  iron  have  to  be  dealt  with  it  is 
advisable  to  make  the  alkaline  treatment  preliminary  to  permit  of  the 
necessary  oxidation;  but  where  sulphates  of  alkaline  earths  only  are  in 
question,  the  requisite  lime  or  alkali  may  be  added  along  with  the 
cyanide  solution.  Where  soluble  iron  salts  are  present  to  any  extent, 
the  washing  should  be  very  thorough,  and  the  solution  should  be  run 
off  from  the  vat  through  a  separate  pipe  which  has  no  connection  with 
any  of  the  cyanide  pipes"  (or  better,  the  washing  should  take  place  in 
a  special  vat;  see  page  49).  "This  matter  of  salts  formed  by  oxidation 
arises  chiefly  in  the  case  of  tailings,  but  it  may  also  happen  with 
concentrates  and  ores,  in  which  case  they  are  treated  as  tailings" 
(MacArthur). 

Butters  and  Clennell  advance  the  following  equations  of  possible 
reactions  accomjianying  the  action  of  cyanide  on  pyrites.  They  illus- 
trate first  the  influence  of  oxygen  on  pyrites: 


THE    CHEMISTRY    OF   THE    PROCESS.  19 

FeSa  +  H2O  +  70  =  FeS04  +  H2SO4 

2  FeS04  H-  0  =  FezOg,  2  SO3  (Wittstein) 

10  FeS04  +  50  =  2  Fe.^0^,  2  SO3  +  3  Fea (804)3  (Berzelius) 

(Basic  sulphate  (Ferric  sulphate 

iusoluble.)  soluble.) 

They  describe,  then,  the  reaction  of  cyanide  on  such  products: 

FeS04  +  2  KCy  =  FeCyg  +  K2SO4 
FeCy2  +  4KCy  =  K4FeCye 

Ultimately  giving  rise  to 

3  K4FeCy6  +  6  FeS04  +  30  =  Fe203  +  6  K2SO4  +  FevCyjg 

Ferric  salts  and  cyanide  give: 

^62(804)3  +  6  KCy  =  Fe2Cye  +  3  K2SO4 
and, 

Fe2Cye  +  6  H2O  =  Fe2(0H)e  +  6  HCy 
Fe2(S04)3  +  6KCy+  6  H2O  =  Fe2(0H)e  +  6  HCy  +  3  K2SO4 

A  mixture  of  ferrous  and  ferric  sulphates  on  addition  of  cyanide  will 
form  Prussian  blue  when  the  ferric  salt  is  in  excess: 

18  KCy  +  3  FeS04  +  2  Fe2(S04)3  =  9  K2SO4  +  Fe4(FeCy6)3 

and  Turnbull's  blue  when  ferrous  salt  is  in  excess: 

12  KCy  +  3  FeS04  +  Fe2(S04)3  =  6  K2SO4  +  Fe3(FeCy6)2 

The  reactions  between  the  various  iron  and  cyanogen  compounds  are 
very  complicated,  and  a  number  of  possible  reactions  have  been  illus- 
trated by  equations  by  various  writers,  the  discussion  of  which  here 
would  take  up  too  much  space. 

In  cases  where  such  conditions  exist,  a  preliminary  washing  with 
water  alone,  or  with  solutions  of  carbonates  or  hydroxide  of  sodium  or 
lime,  as  described,  may  be  not  only  useful  but  imperative.  A  great  sur- 
plus of  alkali  should  be  avoided,  on  account  of  its  action  on  the  zinc  in 
the  precipitation  boxes.  The  loss  of  zinc  will  be  larger  the  greater  the 
alkalinity  of  the  solution;  besides  this,  it  is  apt  to  form  a  sulphide  of 
sodium  or  potassium  with  the  sulphur  of  ores,  which  interferes  with  the 
extraclion  of  the  silver.  Further  careful  scientific  researches  in  refer- 
ence to  secondary  reactions,  which  accompany  the  cyanide  process,  will 
probably  lead  to  technically  important  results.  The  chemistry  of 
precii)itating  the  metals  from  cyanide  solution  will  be  discussed  in  con- 
nection with  the  description  of  the  various  methods  employed  for  that 
purpose. 


20  THE    CYANIDE    PROCESS. 

IV.     DEMONSTRATION    OF    THE    PROCESS  — METHODS    OF 

OPERATION. 

The  cyanide  process  is  worked  either  by  agitating  the  ore  with  the 
solution  ("the  agitation  process"),  or  by  allowing  the  solution  to  pass 
through  the  ore  ("the  percolation  process"). 

A.    The  Agitation  Process. 

When  cyanide  treatment  of  ores  was  first  attempted,  it  was  done  by 
agitating  the  material  under  treatment  with  cyanide  solution;  Rae's 
cyanide  process  of  1867  and  Simpson's  process  of  1885  were  agitation 
processes.  Generally  speaking,  agitation,  as  compared  with  percolation, 
expedites  and  in  instances  increases  extraction,  but  it  requires  motive 
power,  which  is  a  source  of  expense.  Wherever  large  quantities  of  ore 
are  being  treated  it  has  been  abandoned  in  favor  of  the  percolation 
process.  It  is  useful,  however,  in  many  instances  where  the  ores  are 
hard  and  dense,  and  of  a  sufficient  high  value  to  pay  for  the  necessary 
motive  power  and  permit  a  convenient  method  of  filtration;  it  is  applied 
where  the  quantities  are  limited  and  is  mostly  used  for  treating  concen- 
trates, or  such  ores  as  make  the  treatment  of  limited  parcels  by  them- 
selves desirable.  The  importance  of  the  cyanide  agitation  process  has 
not  been  so  fully  recognized  as,  in  some  instances,  it  deserves.  It  is 
natural  that  if  percolation  gives  as  cheaply  the  same  results  it  will  be 
preferred,  but  sometimes  the  agitation  system  has  the  advantage  of 
giving  quicker,  higher,  and  cheaper  returns.  Some  ores,  particu- 
larly ores  containing  tellurides  and  sulphide  of  silver,  give  better 
results  by  agitation  than  by  percolation.  The  agitation  process,  in  its 
present  form,  is  not  well  adapted  to  handling  very  large  quantities  of 
ore  without  a  considerable  outlay  of  machinery.  Technical  improvements 
of  the  system,  which  in  suitable  cases  may  make  the  whole  process  almost 
a  continuous  one,  may  be  expected.  The  chief  appliances  for  the  agita- 
tion process  are  the  agitator  and  the  filter.  Although  any  vat  fitted 
with  revolving  arms  and  barrels,  similar  to  those  employed  in  chlori- 
nation,  may  be  used  successfully  for  agitation,  still  an  agitator  which 
permits  a  charge  and  discharge  quickly  and  safely,  which  has  the  least 
wear  and  tear,  does  absorb  neither  gold  nor  cyanide,  and  is  cheap  in  its 
first  cost,  corresponds  best  with  all  requirements.  I  have  been  using 
wooden  barrels,  wooden  vertical  agitators,  iron  pans,  and  steel  cylindri- 
cal agitators,  and  have  found  the  latter  construction  best  suited  to  the 
purpose  and  satisfying  all  the  above  conditions.  (For  description  of 
such  an  agitator,  see  Utica  cyanide  plant,  page  89.)         ^ 

For  the  purpose  of  extraction,  the  ore  and  the  cyanide  solution  are 
agitated  for  a  time,  varying  in  accordance  with  the  character  of  the  ore, 
generally  ranging  from  six  to  twelve  hours.  I  have  extracted  from  com- 
plex ores,  in  some  instances,  upwards  of  90  per  cent  of  the  assay-value 
in  less  than  two  hours,  and  in  other  instances  I  have  found  it  necessary 
to  continue  the  operation  for  twenty-four  hours.  No  general  rule  can 
be  given;  each  case  has  to  be  investigated  and  the  modus  operandi  to  be 
selected  according  to  circumstances.  (See  table  showing  rate  of  extrac- 
tion in  relation  to  time  of  agitation,  attached  to  the  description  of  the 
Utica  plant,  page  94.)     The  strength  of  the  cyanide  solution  and  the 


DEMONSTRATION    OF    PROCESS METHODS    OF    OPERATION.  21 

volume  required  depend  entirely  on  the  character  of  the  ore;  as  a  rule, 
solutions  for  agitation  should  be  stronger  than  those  for  percolation. 
Here,  like  in  other  matters  in  connection  with  cyanide  treatment,  experi- 
mental investigation  has  to  advise  on  best  conditions.  (See  chapter  on 
laboratory  work,  page  44.)  In  using  barrels  as  agitators,  ore  and  solu- 
tion will  be  charged  before  the  barrel  is  revolved;  if  vertical  vessels  are 
used,  the  solution  will  be  charged  first,  then  the  stirrer  Avill  be  set  in 
motion,  and  the  ore  added  by  degrees. 

When  the  extraction  is  completed,  the  mass  in  the  agitator  is  dis- 
charged, and  the  cyanide  solution,  now  containing  the  gold,  is  separated 
from  the  solid  material — i.  c,  the  residues — by  any  method  which  local 
conditions  and  the  character  of  the  ore  suggest.  Apparatus  of  different 
principles  have  been  used  for  this  purpose.  Filter  presses  of  various 
constructions,  vacuum  filters,  and  centrifugal  machines  have  been 
employed.  Concentrates,  coarse  and  slimy,  can  be  successfully  treated 
by  means  of  my  vacuum  filter  (see  description  of  Sylvia  and  Utica 
plants,  p.  79  and  p.  89),  which  permits  a  quick  filtration  and  a  perfect 
and  speedy  washing  of  the  residues  with  a  minimum  of  liquid.  In  some 
instances  I  made  successful  use  of  centrifugal  force  for  separating  the 
gold  solution  and  washing  the  residues.  For  washing,  weak  cyanide 
solutions  from  previous  operations  are  used,  and  finally  a  water-wash  is 
given.  The  residues  are  then  discharged.  The  gold  solutions  should, 
for  practical  reasons,  be  kept  separate  according  to  their  strength  in  gold 
and  cyanide;  they  pass  through  such  appliances  as  are  used  for  precipi- 
tating the  gold  and  silver,  after  which  the  "liquors"  are  collected  in 
sumps  for  use  on  subsequent  charges  of  ore.  In  well-appointed  works 
no  cyanide  solution  is  allowed  to  run  to  waste,  as  the  same  amount  of 
liquid  remains  constantly  in  circulation. 

The  author  took  out  early  in  1893  a  caveat  in  New  Zealand  for  a  cen- 
trifugal apparatus,  agitator  and  separator  combined,  for  the  treatment 
of  slimy  ores  by  agitation  with  cyanide,  and  subsequent  separation  of 
the  gold  solution  by  centrifugal  force  in  the  same  apparatus.  Experi- 
ments have  of  late  been  made  in  the  Thames  School  of  Mines,  New 
Zealand,  with  the  treatment  of  slimy  ores  by  the  agitation  process  in  an 
apparatus  which  is  described  as  follows:  The  appliances  used  in  the 
operation  consist  of  a  shallow  circular  vat,  a  vacuum  cylinder,  and  an  air 
pump.  The  vat  is  provided  with  four  revolving  arms,  to  which  soft  rubber 
brushes  are  fixed.  The  bottom 'of  the  vat  is  fitted  with  a  false  bottom, 
constructed  of  a  wooden  grating  covered  with  wool  packing.  The  opera- 
tion is  conducted  as  follows:  The  leaching  solution,  made  up  to  the  re- 
quired strength,  is  first  conducted  into  the  vat.  The  revolving  arms  are 
then  set  in  motion,  and  the  dry  pulp  or  slimes  introduced.  The  agitation 
is  continued  for  six  hours,  or  until  the  extraction  is  complete.  A  stopcock 
in  a  pipe  connecting  the  false  bottom  of  the  leaching  vat  and  vacuum  cyl- 
inder, is  then  opened  and  the  air  pump  started.  The  effect  is  immediate. 
At  once  the  clear  solution  begins  to  drain  over  into  the  cylinder,  the  revo- 
lution of  the  arms  preventing  the  slimes  from  settling  and  choking  up 
the  filter  cloth.  When  the  slimes  have  been  drained  down  to  a  thick 
paste,  the  first  wash  water  is  added,  the  pump  again  started,  and  the 
slimes  drained  as  before.  The  water-washings  are  carried  on  in  the  same 
way,  and  when  completed  a  plug  or  door  is  opened  and  the  leached 
slimes  are  sluiced  out.  The  whole  operation  of  leaching  takes  from 
eighteen  to  twenty-four  hours.     The  technical  and  economical  practi- 


22  THE   CYANIDE   PROCESS. 

cability  of  this  method  of  treating  slimy  ores  appears  doubtful  and  will 
have  to  be  proved. 

B.    Percolation  Process. 

Percolation  is  the  method  generally  in  use.  It  is  being  worked  in  the 
United  States,  in  the  British  Colonies  of  Australasia,  and  on  a  very  exten- 
sive scale  in  the  South  African  gold  fields,  and  therefore  merits  a  full 
description.  Percolation  consists  in  soaking  cyanide  solution  through 
ore.  The  character  of  the  material  to  be  treated,  whether  ores,  concen- 
trates, or  tailings,  will  demand  certain  modificatioms  of  the  treatment, 
without  interfering  with  the  principle. 

(a)  Percolation  of  Ores. — It  is  advisable  to  dry-crush  the  ores; 
the  less  dust  produced  the  better  for  percolation.  Screens  of  thirty  meshes 
to  the  lineal  inch  will  be  found  satisfactory  in  most  instances;  in  some 
cases  a  coarser  screen  may  do,  or  a  finer  one  may  be  required.  It  is 
desirable  to  crush  as  coarse  as  possible  without  interfering  with  the 
percentage  of  extraction.  Stamps  are  much  in  use  for  dry-crushing; 
mortars  with  double  discharge  will  give  more  product  and  less  dust. 
Rolls  are  to  be  preferred,  on  the  ground  of  their  giving  a  product  of 
greater  uniformity.  The  ore  is  charged,  either  directly  or  through  hop- 
pers, into  the  vats  in  which  the  percolation  is  conducted.  These  vats, 
or  tanks,  may  be  constructed  of  wood,  brick  and  cement,  concrete,  iron, 
or  steel,  and  vary  in  size  in  accordance  with  local  circumstances  and 
requirements.  The  largest  in  existence  are  the  circular  brick  vats  at 
the  Langlaagate  Estate  and  Block  B  Company's  works  in  Johannes- 
burg; these  vats  have  a  capacity  of  about  400  tons,  and  are  40  ft.  in 
diameter  by  10  ft.  deep.  A  size  in  common  use  in  Johannesburg  is  20 
ft.  in  diameter  and  about  6^  ft.  in  depth,  inside  measurement,  of 
which  I  give  Mr.  J.  S.  Mac  Arthur's  description:  "This  vat  is  made  of 
the  best  white  pine;  the  staves  are  7  ft.  3  in.  long,  4  in.  wide,  and  2^  in. 
thick,  and  fitted  with  a  slight  taper  upwards,  so  that  the  diameter  at 
the  top  is  about  4  in.  less  than  it  is  at  the  bottom.  The  bottom  is  made 
of  the  same  kind  of  material,  but  is  at  least  3  in.  thick.  The  pieces  are 
fitted  together  with  dowel  pins;  it  is  then  fitted  into  a  groove  cut  in  the 
staves  about  6  in.  above  the  ground,  and  the  whole  vat  is  bound  together 
by  steel  hoops  with  a  6  in.  over-lap  an4  at  least  three  rivets.  No  white 
lead  or  packing  of  any  kind  should  be  used  in  making  these  vats.  If 
the  faces  of  the  wood  are  true  no  amount  of  white  lead  or  other  packing 
can  make  them  truer;  if  they  are  not  true,  neither  white  lead  nor  any 
kind  of  packing  will  secure  tightness.  Besides  this  the  cyanide  solution 
being  alkaline  would  quickly  combine  with  and  remove  the  oil  of  the 
white  lead,  if  such  were  used,  and  make  the  vat  positively  worse  than  if 
none  had  been  employed.  Circular  pieces,  cut  out  of  the  solid  wood  and 
not  bent  by  steam  or  moisture,  are  fixed  by  screws  on  the  bottom  of  the 
vat,  about  1  in.  from  the  staves,  all  around  the  circumference.  These 
circular  pieces  are  about  3  in.  thick  and  3  in.  wide,  but  the  length  of  each 
is  immaterial,  provided  always  that  a  complete  ring  is  formed.  Wooden 
slats,  about  1  in.  thick  and  3  in.  high,  are  fixed  about  6  in.  apart  all  over 
the  bottom;  and  an  iron  pipe,  generally  2  in.  in  diameter,  is  screwed  in 
from  the  under  side  near  the  center  point.  The  3  in.  space  from  the 
bottom  to  the  top  of  the  slats  is  filled  in  with  round  and  clean  pebbles. 
Over  this  surface,  formed  by  slats  and  pebbles  alternately,  is  stretched 


DEMONSTRATION   OF   PROCESS — METHODS   OF   OPERATION. 


23 


txi: 


24  THE    CYANIDE    PROCESS. 

a  canvas  cloth  to  act  as  a  filter,  which  is  fastened  by  stretching  it  over 
a  circle  piece  and  ramming  the  cloth  tight  by  pressing  an  inch  rope  into 
the  space  between  the  circle  pieces  and  the  staves.  The  canvas  filter  is 
made  by  shaping  and  sewing  the  canvas  into  a  circle  piece  rather  larger 
than  the  area  of  the  vat  bottom.  In  practice  the  canvas  filter  is  often 
protected  by  covering  it  with  old  sacks  or  cocoa  matting,  which  serves  to 
protect  the  filter  proper  from  the  wear  and  tear  caused  by  the  friction  of 
the  ore  or  by  the  cutting  of  spades."  (Special  vat  and  tank  construc- 
tions will  be  given  aside  from  this  general  description  in  reviewing  large 
and  successful  plants  in  different  countries.)  "The  vat  thus  protected 
and  fitted  is  charged  with  ore,  and  the  cyanide  solution  is  run,  prefer- 
ably from  the  bottom,  by  a  pipe  and  rises  slowly  through  the  crushed 
ore.  It  must  not  be  allowed  to  rush  in  or  rise  violently,  as  by  so  doing 
channels  will  be  formed  through  which  the  solution  will  pass  without 
acting  on  the  ore.  Such  channels  are  apt  to  be  formed  under  any  cir- 
cumstances, and  should  always  be  guarded  against.  After  the  upward 
percolation,  the  stopcocks  are  shut,  and  opened  again  after  the  desired 
time  of  contact  has  passed,  so  as  to  allow  of  a  reversal  and  downward 
percolation.  The  cyanide  solution  now  containing  gold  is  carried 
through  the  precipitating  appliances  and  from  there  into  the  sump,  from 
which  it  may  again  be  used  for  percolation.  It  is  not  wise  to  attempt 
to  make  the  solution  very  rich  in  gold,  and  it  is  considered  better  prac- 
tice to  remove  the  gold  frequently,  as  it  is  found  that  a  cyanide  solution 
containing  gold  is  not  so  active  as  a  similar  solution  without  any." 

In  some  instances,  however,  it  has  been  found  of  advantage  to  use 
gold  cyanide  solution  over  again,  without  first  passing  the  same  through 
the  precipitation  boxes.  (See  experiments  made  by  the  Robinson  Com- 
pany, in  Johannesburg,  page  65.)  According  to  the  richness  of  the  ore 
and  the  fineness  of  the  grinding,  percolation  may  be  repeated  several 
times,  but  after  the  final  percolation  with  the  ordinary  cyanide  solution,, 
a  washing  of  weak  or  waste  solution  should  follow,  and  the  whole  opera- 
tion be  completed  by  a  water-wash,  after  which  the  residues  are  discharged. 
The  filling  and  discharging  can  be  done  either  by  hand  or  by  mechanical 
appliances.  The  various  methods  will  be  described  in  connection  with 
the  process  in  South  Africa. 

(b)  Tailings  are  treated  in  substantially  the  same  way  as  ores,  and, 
the  quantities  being  large  and  the  grade  low,  the  vats  of  the  largest  size 
and  the  most  complete  arrangements  for  saving  labor  in  charging  and 
discharging  are  necessary  for  profitable  working;  generally  speaking,  the 
difficulty  of  discharging  the  vats  is  increased  by  the  increase  of  their 
diameter  and  their  depth.  "  Several  difficulties  arise  in  the  case  of  tail- 
ings, which  do  not  usually  present  themselves  with  ores.  These  diffi- 
culties are  chemical  and  mechanical.  The  chemical  difficulties  have 
been  described  in  the  chapter  on  chemistry;  no  general  rules  can  be 
applied  to  them;  each  case  has  to  be  investigated  and  steps  be  taken 
accordingly.  The  mechanical  difficulties  arise  from  the  tailings  being 
derived  from  the  operation  of  wet-crushing.  When  tailings  are  charged 
in  a  wet  state  into  the  percolating  vat,  they  are  apt  to  remain  in  lumps, 
from  which  the  water  has  to  be  expelled  by  the  cyanide  solution  before 
the  latter  can  effectually  do  its  work.  It  is  obvious  that  where  tailings 
are  already  saturated  with  water,  the  cyanide  solution  will  have  a  diffi- 
culty in  penetrating,  and  this  difficulty  is  increased  when  the  wet  tailings 


DEMONSTRATION    OF   PROCESS — METHODS    OK    OPERATION.  25 

are  held  together  in  masses  between  which  the  cyanide  finds  an  easier 
channel  for  flowing  than  by  soaking  through  them.  This  is  merely  a 
form  of  the  channels  above  referred  to.  Assuming,  however,  that  these 
channels  are  not  formed,  the  tailings  in  a  wet  state  mass  or  pack  together 
to  such  an  extent  as  seriously  to  retard  percolation.  Another  difficulty 
which  arises  from  the  tailings  being  wet  is  that  in  clayey  ores  the  slimy 
portion  of  the  mass  is  apt  to  gather  into  a  layer  by  itself,  which  if  formed 
of  real  clay,  not  only  impedes  but  absolutely  prevents  percolation.  In 
order  to  overcome  this  difficulty  the  simple  method  of  drying  and  mixing 
should  be  adopted.  The  drying  is  a  mere  preliminary  to  the  essential 
of  thorough  mixing.  Particles  of  clay,  which  are  not  kept  apart  by 
sand,  will  agglomerate  and  form  water-proof  strata.  It  is  impossible, 
unless  the  whole  material  is  perfectly  dry,  to  get  the  particles  of  clay 
separated  from  each  other  and  allow  the  sand  particles  to  intervene. 
Even  when  this  is  done,  the  tendency  of  the  clay  particles  to  agglomerate 
must  be  guarded  against  and  prevented.  The  principal  precaution 
necessary  is  that  the  solution,  whether  applied  from  top  or  bottom,  should 
not  flow  more  quickly  than  the  dry  tailings  can  absorb  it.  In  many 
respects  upward  percolation  has  an  advantage,  but  principally  because 
the  flow  of  solution  is  against  gravitation.  In  downward  percolation, 
where  the  flow  of  solution  and  gravitation  act  together,  the  whole  material 
tends  to  become  compressed  into  a  cement,  through  w^iich  the  solution 
penetrates  but  slowly,  preferring  to  take  the  easier  course  down  the  sides 
of  the  vat,  and  in  fact  going  around  rather  than  through  the  tailings. 
Alternate  upward  and  downward  percolation  may  be  found  useful  in 
some  cases." 

The  percolation  vats  are  charged  with  tailings  to  within  a  few  inches 
from  the  top,  and  their  surface  is  leveled.  The  cyanide  solution  of,  say 
from  0.2  to  0.8  per  cent  of  strength,  is  then  permitted  to  penetrate  the 
tailings,  till  the  liquid  covers  them.  The  contents  of  the  vat  will  settle 
some  inches,  which  shrinkage  depends  on  the  depth  of  the  vat  and  the 
percentage  of  moisture  in  the  material.  The  solution  is  permitted  to 
remain  undisturbed  in  contact  for  say  twelve  hours;  after  that  time  it 
is  allowed  to  drain  ott".  As  the  liquid  is  drawn  off,  it  is  replaced  by 
fresh  solution.  This  operation  is  continued  for  a  longer  or  shorter 
period  in  accordance  with  the  value  of  the  tailings  (about  six  to  twelve 
hours  in  the  works  of  the  Robinson  Company  at  Johannesburg).  After 
this  time,  which  is  termed  the  "strong  solution  leaching,"  a  weaker 
solution,  containing  say  from  0.2  to  0.4  per  cent  of  cyanide,  is  turned 
on,  which  filters  through  the  ore  for  about  eight  to  ten  hours.  This 
weak  solution,  when  drawn  off,  is  treated  separately  (see  above).  At 
last,  water  is  run  on  the  tailings  for  replacing  the  last  weak  cyanide 
solution.  The  volume  of  solution  in  constant  use  and  circulation 
remains  the  same.  The  weak  cyanide  solution  is  the  liquor  which  has 
previously  passed  through  the  process  by  which  the  gold  and  silver  are 
precipitated  and  has  from  the  sumps  been  pumped  back  into  the  vat. 

The  percolation  vats,  which  used  to  be  square,  are,  in  new  works, 
round.  The  cyanide  solution  of  the  described  strength  has  no  appre- 
ciable deleterious  effect  either  on  the  wood  of  the  vats  or  on  the  iron 
pipes  and  iron  valves  of  the  pumps.  Iron  or  steel  vats  may  be  protected 
by  a  coating  of  coal  tar  and  asphalt,  or  a  solution  of  asphalt  in  turpen- 
tine, preferably  put  on  hot,  if  special  reasons  make  such  protection 
desirable.     The  quantity  of  cyanide  solution  used  for  the  treatment  of 


26 


THE   CYANIDE   PROCESS. 


PLA  NT 

TO   TREAT 

A  MINIMUM  OF  2000  TONS. 
PER    MONTH. 

SaaZe.  of  Fe&t, 


one  ton  of  tailings  amounts  generally  to  half  a  ton  of  strong  solution 
and  half  a  ton  of  weak  solution  and  wash. 

When  the  percolating  process  is  finally  completed,  the  exhausted  tail- 
ings, or  "residues,"  are  discharged  in  older  works  by  being  shoveled  out 
over  the  side.  More  modern  works  have  trap-doors  at  the  bottom  of 
their  vats  for  discharge  (see  diagram,  page  59).  "Sluicing  out"  of  the 
residues  is  being  practiced  in  several  localities.  The  large  vats  of  the 
Langlaagte  Estate  Company's  works  at  Johannesburg,  which  hold  400 
tons  of  tailings  each,  are  discharged  by  means  of  running  cranes  (see 
diagram,  page  57). 

It  must  be  always  borne  in  mind  that  the  most  complete  arrangements 
for  saving  labor  in  charging  and  discharging  large  quantities  of  low- 
grade  material  are  necessary  for  profitable  working.  In  order  to  achieve 
that  end,  a  plant  should  offer  all  such  facilities  which  circumstances 
permit;  it  should  be  so  arranged  that  the  tailings  will  not  have  to  be 
lifted,  but  can  be  dumped  into  the  percolation  vats.  The  size  of  the 
vats  has  been  constantly  increased.  New  works,  like  the  Roodeport 
works  at  Johannesburg,  are  supplied  with  vats  40  ft.  in  diameter.  The 
table  appended  illustrates  the  dimensions  of  the  percolation  vats  in  some 
of  the  more  important  cyanide  extraction  plants: 


DEMONSTRATION    OF    PROCESS — METHODS    OF    OPERATION. 


27 


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28  THE   CYANIDE    PROCESS. 

All  vats  should  be  some  distance  above  the  ground,  so  that  leaking 
can  be  easily  detected;  concrete  foundations  for  the  vats  are  generally 
adopted.  The  wooden  tank  material  is  an  absorbent  of  both  cyanide 
and  gold,  particularly  when  new.  It  has  been  found  at  the  Salisbury 
works,  Johannesburg,  that  pine  wood  lying  thirty-four  hours  in  a  0.3 
per  cent  cyanide  solution  reduced  it  to  0.05  per  cent,  while  cement  reduced 
it  to  0.24  per  cent.  Cement  tanks  have  come  into  use  of  late,  and  have 
proved  satisfactory;  such  tanks  and  vats  may  advantageously  be  built 
into  excavations  in  solid  ground.  Many  attempts  have  been  made  to 
discharge  tailings-pulp  direct  from  the  plates,  or  ore-pulp  direct  from 
the  mortars  into  the  percolating  vats,  but  their  successful  treatment  by 
cyanide  when  so  discharged  has  been  prevented  by  mechanical  causes, 
the  reason  being  that  the  material  packs  so  densely  in  the  vats  that  it 
makes  percolation  an  extremely  tedious  operation,  and  in  consequence  of 
the  presence  of  slimes  the  results  are  unsatisfactory.  The  advantages 
of  wet-crushing  over  dry-crushing  are,  from  an  economical  standpoint, 
so  obvious,  however,  that  experiments  will  be  continued,  and  ultimately 
the  drawbacks  which  now  adhere  to  the  method  may  be  overcome. 
Cyanide  of  potassium  solution  has  been  used,  in  some  instances  and  in 
an  experimental  way,  in  lieu  of  water  in  the  mortars,  when  wet-crush- 
ing was  resorted  to,  but  does  not  appear  to  be  practiced  anywhere  at 
present.  An  innovation  in  percolation  consists  in  the  circulating  system, 
which  will  be  described  in  detail  in  connection  with  the  practice  of  the 
cyanide  process  in  South  Africa  (see  page  46). 

(c)  Percolation  of  Concentrates. — "These  are  treated  similarly  to 
ores,  but  being  generally  richer  require  a  greater  number  of  percola- 
tions, and  thereby  a  much  longer  time.  In  most  cases,  their  quantity 
is  limited,  and  the  size  of  the  percolation  vats  varies  in  accordance 
with  the  quantity."  I  have,  in  most  cases,  given  agitation  the  prefer- 
ence to  percolation  for  treatment  of  concentrates,  on  account  of  its 
greater  cheapness  and  rapidity;  in  Africa  most  companies  prefer  the 
latter  method.  Percolation  of  concentrates  requires  about  twenty  days, 
the  reason  for  which  will  be  found  partly  in  the  coarser  character  of  the 
gold,  partly  in  its  being  in  the  form  of  amalgam,  and  mainly  in  the 
difficulty  the  solution  has  in  penetrating  between  the  faces  of  the  sul- 
phuret  crystals.  A  difficulty  sometimes  arises  in  the  percolation  of 
concentrates,  owing  to  the  crystalline  form  of  iron  pyrites  and  galena. 
These  minerals  crystallize  in  cubes,  and  when  suspended  partially  or 
wholly  in  a  fluid  tend  to  range  themselves  face  to  face,  so  that  a  section 
of  such  a  mass  deposited  from  a  fluid  would  resemble  a  brick  wall  in 
structure.  This  difficulty  does  not  arise  in  the  case  of  sand  or  minerals 
which  crystallize  in  other  systems.  Whenever  it  occurs,  it  may  be  over- 
come by  mixing  the  cubical  sulphurets  with  coarse  sand. 

C.     Cyanide  and  Cyanide  Solutions. 

The  best  strength  of  solutions  to  use  in  either  percolation  or  agitation 
depends  entirely  upon  the  nature  of  the  ore,  and  it  is  impossible  to  set 
any  rule.  The  strength  of  solutions  generally  used  varies  from  one 
eighth  to  one  per  cent  of  cyanide.  (In  reference  to  the  determination  of 
the  correct  strength  to  be  used  in  treating  any  class  of  ore,  see  chapter 
on  laboratory  work,  page  44.)     "  For  convenience  and  economy  of  work, 


DEMONSTRATION    OF   PKOCESS — METHODS    OF    OPERATION.  29 

the  solutions  are  generally  divided  into  three  classes:  No.  1,  No.  2,  and 
No.  3,  of  which  No.  1  is  the  strongest  and  No.  3  the  weakest.  Assuming 
that  the  material  under  treatment  does  not  require  a  preliminary  alka- 
line wash,  or  that  such  treatment  has  already  been  completed,  it  is  usual 
to  run  on  a  weaker  solution,  say  No.  2,  in  the  first  place,  and  after  its 
percolation  to  use  No.  1,  and  then  No.  3  in  the  same  manner,  finishing 
with  a  water-wash,  the  first  portion  of  which  is  run  into  and  forms  part 
of  the  No.  3  solution.  These  different  solutions  are  kept  separate  after 
percolation,  and  when  charged  with  gold  are  subjected  by  themselves  to 
the  precipitating  process.  In  some  works  sumps  are  used  as  reservoirs, 
and  the  solution  is  pumped  direct  from  them  onto  the  ore;  but  space 
permitting,  it  is  considered  better  practice  to  have  reservoirs  for  each  solu- 
tion above  the  percolation  vats,  from  which  the  flow  can  be  more  easily 
regulated."  For  the  purpose  of  bringing  weak  solutions  up  to  a  certain 
standard,  it  is  advisable  to  use  a  very  strong  solution,  of  which  enough 
is  added  to  bring  the  weak  solution  up  to  the  required  strength.  This 
method  has  to  a  great  extent  taken  the  place  of  the  old  method  of  using 
solid  cyanide  to  bring  weak  solutions  up  to  high  standards.  The 
strength  of  the  cyanide  solutions,  which  it  is  of  great  economical  impor- 
tance to  determine,  is  tested  according  to  Liebig's  method  by  means  of  a 
one  tenth  standard  solution  of  nitrate  of  silver,  which  is  made  by  dis- 
solving seventeen  grams  of  pure  nitrate  of  silver  in  one  litre  (1,000  cc.) 
of  distilled  water.  Liebig's  method  is  based  on  the  fact  that  silver 
cyanide  is  soluble  in  excess  of  potassium  cyanide,  with  formation  of  a 
double  cyanide  of  silver  and  potassium: 

KCy       +       AgN03        =       AgCy        +        KNO3 

(Potassic  cyanide.)    (Argentic  nitrate.)    (Argentic  cyanide.)    (Potassic  nitrate.) 

AgCy         +         KCy  =  KAgCy^ 

(Argentic  cyanide.)      (Potassic  cyanide.)         (Argentic  potassic  cyanide.) 

As  soon  as  the  whole  of  the  cyanide  has  been  converted  into  a  soluble 
silver  salt,  an  additional  drop  of  silver  nitrate  will  produce  a  permanent 
precipitate  of  the  insoluble  simple  cyanide  of  silver: 

KAgCya         +        AgNOs      =      KNO3        +       AgCy 

(Argentic-potassic  cyanide.)    (Argentic  nitrate.)    (Potassic  nitrate.)    (Argentic  cyanide.) 

A  measured  portion  of  the  perfectly  clear  cyanide  solution  which  is  to 
be  tested  is  taken;  if  necessary  some  distilled  water  is  added,  and  the 
standard  silver  solution  is  gradually  added  from  a  graduated  burette, 
until  a  permanent  white  cloud  is  formed.  As  each  cubic  centimetre  of 
the  silver  solution  is  equal  to  0.013  grams  of  potassium  cyanide,  by 
multiplying  the  number  of  cubic  centimetres  consumed  by  0.013  the 
amount  of  cyanide  in  the  solution  tested  is  found  in  grams,  from  which 
the  percentage  can  easily  be  calculated.  A  convenient  silver  solution 
for  the  purpose  of  analyzing  cyanide  solutions  is  one  of  such  strength 
that  every  cc,  added  to  10  cc.  of  the  solution  which  is  to  be  tested,  cor- 
responds with  1  per  cent  pure  cyanide  of  potassium.  "The  cyanide 
solutions  are  apt  to  form,  by  continued  exposure  to  the  air,  carbonate  of 
ammonia;  and  as  this  salt  interferes  very  seriously  with  the  determina- 
tion of  the  cyanide,  it  is  well  to  add  a  few  drops  of  solution  of  iodide  of 
potassium,  which   forms   a   pale-yellow  cloud  insoluble   in   ammonia, 


30  THE    CYANIDE   PROCESS. 

which  indicates  completion  of  the  reaction"  (MacArthur).  The  mode 
of  analysis,  as  described  above,  calculates  the  amount  of  cyanide  of 
potassium  in  a  solution  by  ascertaining  its  contents  of  cyanogen.  If  the 
cyanogen  is  partly  combined  with  sodium  instead  of  potassium,  the  per- 
centage of  cyanide  appears  in  the  analysis  higher  than  it  really  is;  the 
value  of  commercial  cyanide  of  potassium  should  therefore  be  ascer- 
tained by  determining  its  contents  of  sodium,  if  any,  as  it  is  possible, 
by  manufacturing  a  mixture  of  cyanide  of  potassium  and  cyanide  of 
sodium,  to  produce  cyanide,  which  according  to  the  ordinary  method  of 
estimation,  contains  apparently  more  than  100  per  cent  of  potassium 
cyanide.  The  analysis  of  cyanide  solutions  for  gold  and  silver  will  be 
described  in  the  chapter  on  laboratory  work  (page  44). 

The  Cyanide  usually  employed  for  ore  extraction  is  of  two  classes,  one 
of  which,  manufactured  in  Scotland,  contains  from  70  to  80  per  cent  of 
pure  potassic  cyanide;  the  other  is  manufactured  in  Germany  and  con- 
tains upwards  of  98  per  cent.  The  latter  grade  is  preferable,  because  it 
contains  no  carbide  of  iron,  the  presence  of  which  in  the  former  not  only 
involves  periodical  cleaning  out  of  the  dissolving  tank,  but  also  is  liable 
to  precipitate  gold  should  any  of  it  come  in  contact  with  gold  cyanide 
solution.  The  price  of  the  best  quality  of  cyanide  of  potassium,  guar- 
anteed to  contain  upwards  of  98  per  cent  cyanide,  is  at  present  50  cents 
per  pound  in  the  United  States,  delivered  at  seaports. 

D.    Treatment  of  the  Gold  Solutions  (Recovery  of  the  Bullion). 

All  methods  of  treating  ores,  as  described,  yield  solutions  containing 
more  or  less  gold  and  more  or  less  cyanide  of  potassium.  The  next 
step  is  to  recover  the  gold  and  silver.  The  chief  method  for  that  end 
consists  in  their  precipitation  by  means  of  finely  divided  zinc;  it  forms 
one  of  the  patent-claims  of  MacArthur  and  Forrest,  and  is  generally  in 
use.  Another  method  is  that  of  B.  C.  Molloy,  of  Johannesburg,  who 
decomposes  the  cyanide  solution  of  gold  by  means  of  an  alkali  metal, 
and  amalgamates  the  bullion  thus  liberated;  cyanide  of  potassium  is 
regenerated  by  this  process.  The  Molloy  process  has  been  in  use  on  a 
small  scale  in  South  Africa,  but  has  apparently  gone  into  disuse  again, 
for  the  official  list  of  the  Chamber  of  Mines  of  Johannesburg  for  March 
does  not  return  any  gold  as  extracted  by  that  process,  as  had  been  the 
case  in  former  months.  Other  processes  for  bullion  precipitation  are: 
The  Siemens  and  Halske  process  of  precipitating  the  noble  metals  by 
electrolysis  on  lead  sheets,  which  method  is  in  use  at  the  Worcester  works 
in  Johannesburg;  the  Pielsticker  process  of  using  electrolysis,  constantly 
applied  to  the  circulating  solution;  the  Moldenhauer  process  of  precipi- 
tation by  means  of  aluminium,  and  the  Johnston  process  of  using  char- 
coal as  reducing  agent.  No  information  is  available  on  the  technical 
application  of  the  three  processes  last  named. 

(a)  Bullion  Precipitation  by  Zinc. — The  solutions  from  the  perco- 
lation vats,  or  from  the  filter  appliances  if  the  agitation  process  is  used, 
are  run  through  boxes  which  are  divided  into  chambers  with  double 
partitions.  The  first  partition  does  not  reach  to  the  bottom  of  the  box, 
the  next  one  not  quite  to  the  top,  and  so  on;  they  compel  the  solution  to 
enter  each  chamber  from  below,  and  pass  through  a  perforated  bottom,. 


DEMONSTRATION   OF   PROCESS — METHODS   OF   OPERATION. 


31 


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32  THE    CYANIDE    PROCESS. 

on  which  the  finely  divided  zinc  is  placed.  After  passing  through  the 
zinc,  the  solution  leaves  the  chamber  at  its  top;  then  it  descends  between 
the  double  partition  to  the  space  below  the  perforated  bottom  of  the  suc- 
ceeding chamber,  where  it  undergoes  the  same  treatment,  and  so  forth 
in  all  successive  ones  (see  sketches,  pp.  31, 33).  "This  arrangement  has 
been  adopted  because  the  gold  is  precipitated  on  the  zinc  in  a  state  of 
fine  division,  and  would,  if  deposited  on  the  upper  surface,  prevent  the 
further  flow  of  the  solution;  but  being  deposited  on  the  under  surface, 
the  gold  precipitate  falls  ofl"  and  leaves  the  passage  clear.  Each  precipi- 
tating box  may  contain  ten  to  twelve  double  chambers,  and  no  matter 
how  rich  the  solution  is  at  the  inflow,  it  should  not  contain  more  than 
a  few  grains  per  ton  at  the  outflow."  In  some  works  the  zinc  boxes  are 
up  to  40  ft.  long.  There  is,  however,  no  advantage  in  going  beyond  a 
limited  number  of  chambers,  as  precipitation  of  the  metals  takes  place 
chiefly  in  the  first  few  compartments  of  the  box.  (See  description  of  tJtica 
plant,  p.  89). 

I  give  here  Mr.  J.  S.  MacArthur's  description  of  his  construction  of 
filter  boxes,  and  the  mode  of  working  them  which  is  used  by  the 
MacArthur-Forrest  patentees  in  South  Africa:  "  The  gold  precipitate  falls 
through  the  gauze  'a'  (see  cut,  p.  31)  into  a  chamber  which  communi- 
cates with  an  inclosed  launder  or  gutter.  From  day  to  day  fresh  zinc  is 
added,  always,  adding  it  in  the  last  chamber  and  bringing  the  partly 
consumed  zinc  up  a  step,  so  that  the  first  chamber  contains  zinc  half 
consumed  and  rich  in  gold,  while  the  last  chamber  contains  fresh  zinc 
containing  no  gold.  At  intervals  of  about  two  weeks,  there  is  a  clean-up, 
and  the  gold  is  collected  by  stirring  the  zinc  so  as  to  cause  the  gold 
precipitate  to  fall  ofl".  When  this  is  done,  the  stopper  '  b '  is  raised  and 
the  gold  precipitates  fall  through  the  opening  into  the  launder  'B.' 
When  this  has  been  completed  for  each  chamber,  the  launder  is  dis- 
charged through  the  opening  '  C  "  The  precipitation  boxes  are  usually 
made  of  wood,  and  although  I  have  been  well  satisfied  with  such  mate- 
rial (kauri-pine  in  New  Zealand),  I  substituted  it  in  California  by  steel, 
which  I  found  in  every  respect  an  excellent  material  for  the  purpose.  I 
could  not  ascertain  any  increased  loss  of  cyanide  by  the  use  of  iron  as 
box  material;  the  galvanic  action  of  iron  and  zinc  in  contact  on  the 
cyanide  seems  by  some  writers  overrated  (see  description  of  Utica  plant, 
p.  89).  Of  this  apparatus,  which  is  based  on  the  same  principle,  but 
which  in  its  construction  is  simpler  than  the  one  described,  I  give  the 
appended  diagram.  The  total  length  of  the  apparatus  is  9  ft.,  the  size" 
of  the  chambers  is  9  in.  by  9  in.  by  14  in.  deep;  the  distance  of  the  par- 
titions between  each  chamber  is  1  in.  The  perforated  and  movable 
false  bottom  of  each  chamber  is  of  steel,  which  is  an  advantage  over  wire 
sieve  bottoms,  which  easily  become  clogged  b}^  bullion.  The  real  bottom 
of  each  chamber  has  a  faucet  of  1  in.  diameter,  which  discharges  the 
liquid  and  the  finely  divided  bullion  into  a  tank  below  the  apparatus, 
from  where,  after  settling  (under  addition  of  some  alum,  if  saving  of 
time  is  an  object),  it  is  transferred  to  a  vacuum  filter,  as  described 
further  on. 

"The  zinc  used  for  precipitation  purposes  should  be  the  best  quality 
found  in  commerce,  and  should  not  contain  arsenic  or  antimony;  a  small 
percentage  of  lead,  however,  does  no  harm,  but  rather  tends  to  promote 
rapid  action  by  forming  a  voltaic  couple  with  the  zinc"  (MacArthur). 
The  metal  is  preferably  used  as  shavings,  or  filiform,  as  these  forms 


DEMONSTRATION    OF    PROCESS — METHODS    OF   OPERATION. 


33 


give  in  practice  the  most  surface  for  the  least  weight  and  do  not  pass 
readily  through  a  sieve,  whereas  the  gold,  which  is  precipitated  as  a  fine 
powder,  does.  Shavings  have  the  advantage  of  not  forming  lumps  so 
easily  in  the  precipitation  boxes  as  filiform  zinc;  the  latter  has,  however, 
the  greater  advantage  of  being  cheaper  in  its  preparation,  as  no  remelt- 
ing  of  the  commercial  zinc  is  required.  It  is  prepared  by  cutting  sheet 
zinc  into  disks,  a  number  of  which  are  placed  together  and  turned  on  a 
lathe  with  an  ordinary  chisel.  The  zinc  linings  of  the  cyanide  packing- 
cases,  for  which  there  is  no  market,  may  be  turned  to  account  in  that 
way. 

3cp 


34  THE    CYANIDE    PROCESS. 

In  reference  to  the  cost  of  preparing  the  zinc,  I  may  quote  the  Nigel 
Gold  Mining  Company  in  Johannesburg,  where  one  native,  working 
about  eight  hours  a  day,  can  easily  keep  the  works  going,  with  an  output 
of  about  two  thousand  ounces  of  gold  monthly;  the  consumption  of 
zinc  is  about  twenty  pounds  daily.  As  a  rule,  one  cubic  foot  of  zinc 
shavings  in  the  precipitating  box  is  sufhcient  for  the  precipitation  of  the 
gold  from  two  tons  of  solution  per  twenty-four  hours,  or,  roughly  speak- 
ing, from  the  same  weight  of  ore  (see  the  zinc  for  bullion  precipitation 
in  Africa  on  page  53).  Zinc  in  sheets  and  granulated  zinc  have  been 
tried  for  bullion  reduction,  but  with  indifferent  results,  on  account  of 
their  limited  surface.  Zinc  amalgam  and  zinc  dust  have  not  answered, 
for  mechanical  reasons — zinc  dust  packing  too  tightly  and  zinc  amalgam 
not  offering  sufficient  surface  in  proportion  to  its  weight.  The  precipita- 
tion of  the  metals  in  the  zinc  boxes  takes  place  rapidly;  the  zinc  in  the 
compartment  near  the  influx  will  be  much  more  quickly  charged  with 
bullion  than  that  in  those  more  distant,  and  the  zinc  will  be  consumed 
in  proportion.  Zinc  on  which  bullion  is  already  deposited  is  more  active 
than  new  zinc;  it  is  therefore  advisable  to  replace  the  dissolved  zinc  in 
the  upper  by  zinc  from  the  lower  chambers,  and  to  add  the  fresh  zinc  in 
the  last  compartment.  The  generation  of  hydrogen  in  the  boxes  is 
liable,  by  polarization,  to  partly  interfere  with  the  bullion  precipitation; 
the  zinc  in  the  boxes  should  be  stirred  up  occasionally  to  avoid  this. 

The  zinc  boxes  are  cleaned  up  once  or  twice  a  month;  for  that  purpose 
the  inflow  of  the  solution  is  stopped.  The  zinc  shavings  are  stirred 
with  a  rod,  which  causes  the  fine  bullion  to  fall  ofl"  and  to  pass 
through  the  perforations  of  the  false  bottoms,  and  through  the  faucets 
at  the  real  bottoms,  into  the  box  below,  where  it  settles  readily,  on 
the  addition  of  a  little  alum.  A  jet  of  water  will  further  wash 
the  zinc  in  the  chambers.  This  method  of  operating  takes  only  a 
few  minutes,  and  has  been  used  by  me  in  California.  The  liquid 
standing  above  the  settled  bullion  is  returned  to  the  zinc  box;  the 
bullion  itself,  unavoidably  mixed  with  fine  zinc,  is  transferred  through 
a  fine  sieve  onto  a  vacuum  filter.  If  a  final  cleaning-up  is  desired,  it 
will  be  necessary  to  dissolve  the  whole  of  the  zinc,  impregnated  with 
bullion,  in  acid;  such  necessity  will,  however,  rarely  arise.  The  manip- 
ulation itself  if  required,  offers  no  difficulties.  The  precipitated  bullion 
is  very  finely  divided,  and  provision  should  be  made  to  prevent  its  flow- 
ing away  with  the  liquid  out  of  the  precipitation  boxes  (see  page  52). 

The  process  of  bullion  precipitation  by  zinc  is,  generally  speaking,  a 
satisfactory  one,  although  not  free  from  objections;  all  operations  with 
and  manipulations  of  the  precipitated  bullion  require  care  to  avoid  loss. 
The  action  of  the  zinc  on  gold  solution  is  theoretically  very  simple — 
a  simple  substitution  of  gold  by  zinc  according  to  the  equation: 

2  KAuCy2    +    Zn     =      K2ZnCy4    -f-     2  Au 

(Auro-potassic  cyanide.)    (Zinc.)      (Zinc-poiassic  cyanide.)     CGold.) 

One  pound  of  zinc  should  precipitate  about  six  pounds  of  gold.  The 
actual  consumption  is,  however,  considerably  larger,  and  amounts  to 
from  5  oz.  to  1  lb.  of  zinc  per  ounce  of  gold  recovered.  A  constant  gen- 
eration of  hydrogen  gas  in  the  precipitation  boxes  proves  the  effect  of 
the  potassic  hydroxide  on  the  zinc,  and  probably  a  decomposition  of 
cyanide  of  potassium,  going  on  parallel  with  the  decomposition  of  the 


DEMONSTRATION    OF   PROCESS — METHODS    OF    OPERATION.  oO 

double  gold  cyanide.  A  considerable  loss  of  zinc  occurs  generally 
in  refining  the  precipitated  bullion,  which  always  contains  a  high 
percentage  of  that  metal.  The  double  salt  of  auro-potassic  cyanide 
appears  to  be  one  of  the  most  stable  of  gold  salts;  its  decompo- 
sition by  zinc  is,  however,  practically  complete;  an  excess  of  cyanide  of 
potassium  in  the  solution  does  not  redissolve  precipitated  gold  in  the 
boxes  as  long  as  there  is  zinc  present.  The  cyanide  of  potassium  formed 
into  a  double  salt  with  zinc  during  the  gold-reducing  process  is  not 
available  for  dissolving  gold  in  new  operations.  If  a  surplus  of  caustic 
soda  has  been  used  for  neutralizing  acid  salts  in  the  ore  without  follow- 
ing washing,  the  loss  of  zinc  will  naturally  be  increased.  A  white  pre- 
cipitate is  constantly  accompanying  the  reduction  of  bullion  in  the  zinc 
boxes,  undoubtedly  the  result  of  the  action  of  alkali  on  the  zinc  and  of 
the  zinc-potassium  oxide  on  the  double  cyanide  of  zinc  and  potassium, 
Avhich  is  always  present  in  the  solution,  forming  the  insoluble  cyanide 
of  zinc;  ferrocyanide  of  zinc  is  also  formed  in  the  boxes.  Ferrocyanide 
of  zinc  is  formed  in  the  percolation  vats  when  the  double  cyanide  of 
zinc  and  potassium  comes  in  contact  with  the  iron  salts  in  the  ore,  and, 
as  it  is  insoluble,  to  this  cause  is  due  the  constant  removal  of  zinc  from 
the  solution  with  the  residues  (Buckland).  The  gold  precipitate  on  the 
zinc  is,  as  a  rule,  brown  to  black,  with  sometimes  a  metallic  luster;  it  is 
mostly  slimy,  and  when  dry  it  seldom  contains  more  tban  40  or  50  per 
cent  of  gold  and  silver,  the  remainder  being  finely  divided  zinc  and  its 
accompanying  impurities,  such  as  carbonate  of  lead.  It  may  also  con- 
tain copper,  if  that  metal  is  present  in  solution.  (In  the  instance  of 
treating  concentrates  containing  carbonate  of  copper  from  the  Sylvia 
Mine,  New  Zealand,  the  gold  solution  contained  a  very  appreciable 
quantity  of  copper;  this  complicated  matters  by  causing  the  copper  to 
precipitate  with  the  gold  and  cover  the  zinc,  thus  forming  a  galvano- 
plastic  coating,  which  made  it  necessary  to  dissolve  the  whole  of  the  zinc 
for  the  purpose  of  obtaining  the  bullion,  till  I  found  an  addition  of 
cyanide  to  the  solution,  before  it  enters  the  zinc  boxes,  useful  for  the 
prevention  of  the  deposition  of  the  copper.) 

I  always  found  mercury  in  the  zinc  bullion  in  not  inconsiderable 
quantities  when  concentrates  had  been  treated  by  agitation;  such  mer- 
cury must  have  been  derived  from  amalgam,  and  mercury  saved  with 
the  pyrites  on  the  concentrators.  Gmelin  and  others  describe  mercury 
as  absolutely  insoluble  in  cyanide.  There  is,  however,  no  doubt  of  the 
correctness  of  my  observations;  the  mercury  must  have  been  dissolved 
in  the  cyanide  solution,  which  entered  perfectly  clear  into  the  zinc  boxes; 
solubility  of  gold  amalgam  in  cyanide  may  offer  the  explanation.  Traces 
of  antimony  and  arsenic  have  also  been  found  in  the  bullion.  The  pre- 
cipitation of  silver  goes  on  by  zinc  simultaneously  with  the  gold;  it  is 
even  more  rapid  and  complete  than  that  of  gold.  (See  my  table  on  the 
process  in  the  Utica  Works,  page  91.) 

Other  apparatus  than  the  described  boxes  have  been  suggested  for 
bullion  precipitation  by  zinc — for  instance,  earthenware  and  porcelain 
vessels  have  been  recommended.  They  have  the  apparent  advantnge  of 
cleanliness;  tbeir  construction,  however,  makes  the  cleaning-up  of  the 
bullion  difficult,  the  connection  between  the  single  cells  being  compli- 
cated; they  have  not  become  a  practical  success  in  works  of  any  extent; 
they  are  all  based  on  the  principle  of  the  solution  penetrating  the  zinc 
from  below  and  running  off  at  the  top.     The  precipitates,  obtained  as 


36 


THE    CYANIDE    PROCESS. 


n 


a 


1 


-4-3- 


described  from  the  zinc  boxes,  are  transferred  to  a  sieve,  made  of  No.  1 
punched  battery  screen  or  a  40-mesh  wire  screen,  through  which  they 
are  washed  onto  a  filter  in  connection  with  a  vacuum  chamber,  where 
they  are  liberated  from  the  adhering  cyanide  solution  and  reduced  from 
their  very  voluminous  state  into  a  more  compact  form.  This  filtration 
will  always  be  found  slow  on  account  of  the  extremely  slimy  character 
of  the  bullion.  For  filtering  and  washing  the  bullion  slimes,  filter 
presses  may  be  suggested.  By  the  screening  process  the  coarser  particles 
of  zinc  are  separated  from  the  bullion,  but  the  bullion  still  contains  a 
large  percentage  of  very  fine  zinc,  of  which  it  is  advisable  to  remove  as 
much  as  possible  before  melting. 

Bullion  Refining. — The  means  for  this  purpose  are  calcination  or 
roasting  and  acid  treatment.  I  use  for  roasting  (see  description  of 
Sylvia  plant,  p.  79)  a  muffle  furnace,  where  the  slimes  are  dried,  and 
then  calcined  for  the  promotion  of  the  oxidation  of  the  base  metals. 
The  calcining  process  is  generally  in  use  in  South  Africa,  and  will  be 
described  with  the  cyanide  practice  in  Johannesburg,  page  54.  I  gener- 
ally prefer  sulphuric  acid  treatment,  with  following  washing  and  drying 
of  the  bullion.  The  acid  treatment  is  a  comparatively  simple  operation, 
and  does  not  require,  even  for  large  quantities  of  bullion,  any  other 
apparatus  than  wooden  tubs,  the  increased  temperature  produced  by  the 
reaction  of  the  acid  on  the  zinc  making  application  of  artificial  heat 
superfluous.  The  separation  of  the  acid  solution  from,  and  the  Avashing 
of,  the  bullion  is  best  done  by  decantation,  and  completed  on  the  bullion 
filter  mentioned  above.  It  is  advisable  to  liberate  the  bullion  as  much 
as  possible  from  base  metal  before  melting,  which  is  otherwise  connected 
with  loss  of  gold  by  evaporation  caused  by  the  volatilization  of  zinc; 
besides,  the  zinc  fumes  are  very  disagreeable.  The  presence  of  oxides 
of  base  metals  (as  obtained  by  calcination)  makes  the  melting  tedious 
and  expensive  on  account  of  the  detrimental  influence  of  the  slag  on 
the  melting  pots.  The  presence  of  a  high  percentage  of  base  oxides  pre- 
vents the  use  of  graphite  crucibles  and  compels  the  use  of  clay  pots. 
Bullion,  when  treated  by  acid  as  described,  does  not  offer  any  difficulties 
in  melting,  if  proceeded  with  in  the  following  manner: 


DEMONSTRATION    OF    PROCESS — METHODS    OF    OPERATION.  37 

The  bullion,  after  having  been  treated  with  sulphuric  acid  and  washed 
with  water,  is  dried  by  suction  on  the  vacuum  filter  as  much  as  pos- 
sible, after  which  it  is  easily  detached  from  the  filter  cloth.  The  mass 
is  then  charged  into  the  muffle  (see  plans  of  Sylvia  cyanide  plant, 
page  77).  The  heat  is  kept  low  to  drive  off  the  moisture;  it  is  then 
increased  gradually  to  dark  red;  after  about  one  hour's  calcination, 
during  which  time  the  oxidation  of  base  metals  which  escaped  removal 
by  acid  treatment  is  going  on,  the  mass  presents  a  gray-brown  appear- 
ance. Attention  has  to  be  paid  to  the  draught  to  prevent  loss  of  the 
fine  precipitates.  Bullion  resulting  from  the  treatment  of  concentrates 
will  invariably  give  off  quicksilver  vapors;  condensation  yielded  only  a 
small  quantity.  The  calcination  process  completed,  the  roasted  bullion 
is  carefully  transferred  from  the  muffle,  by  means  of  a  small  shovel,  into 
a  wrought-iron  box  for  cooling  purposes.  It  now  presents  itself  in  the 
form  of  lumps,  approaching  more  or  less  the  spherical  form,  of  the  size 
of  peas,  largely  mixed  with  dust.  When  sufficiently  cooled,  it  is  charged 
into  a  pulverizing  cylinder  of  sheet-iron,  3  ft.  long  and  2  ft.  in  diameter, 
which  is  revolved  by  means  of  a  pulley.  Large  pebbles  are  charged  into 
the  apparatus  with  the  bullion  to  aid  pulverization.  Borax,  with  prefer- 
ence borax  glass,  and  soda  ("ammonia-process  soda")  are  added  into 
the  barrel,  in  proportions  according  to  experience,  for  securing  a  fusible 
clear  slag  of  light  specific  gravity.  If  the  bullion  is  base  on  account 
of  a  large  proportion  of  zinc  oxide,  which  happens  only  if  acid  treat- 
ment was  not  properly  conducted,  a  silicious  flux,  like  sand  or  glass, 
has  to  be  added.  Acid  sulphate  of  soda  and  fluorspar  have  been  occa- 
sionally found  useful  as  additional  fluxes.  During  pulverization,  a 
thorough  mixture  of  bullion  and  fluxes  will  take  place.  Moisture  in 
the  fluxes  should  be  avoided,  as  it  is  a  certain  source  of  loss  in  melting, 
the  escaping  water  carrying  fine  bullion  out  of  the  pot. 

Plumbago  crucibles  are  very  well  adapted  for  melting  bullion,  pre- 
pared as  above  described;  they  stand  almost  as  many  operations  as  with 
battery  gold.  In  melting,  some  borax  is  first  put  into  the  crucible;  the 
bullion  mixture  from  the  pulverizing  and  mixing  cylinder  is  not  added 
all  at  once,  but  as  e,ach  portion  melts  and  sinks  down,  fresh  quantities 
of  it  are  put  in.  The  melting  goes  on  speedily  and  in  the  most  satisfac- 
tory manner.  When  the  whole  quantity  is  finally  charged,  the  tempera- 
ture is  kept  very  high  for  some  time,  to  give  the  small  bullion  globules 
a  chance  to  collect.  The  contents  of  the  pot  are  poured  into  a  heaf-ed 
mold  in  the  usual  manner.  No  chemical  losses  will  be  experienced  by 
this  method  of  bullion  melting.  Bullion  obtained  by  the  described 
manipulation  will  be  found  to  be  at  least  950  fine.  The  bullion  pi'o- 
duced  by  cyanide  works  generally  varies  in  fineness  according  to  the 
attention  paid  to  its  refining.  Gold  purchasers  buy  bullion  on  assay, 
and  refiners  charge  higher  rates  for  baser  bullion;  it  is  therefore  as  a 
rule  cheaper  in  the  end  to  produce  clean  bullion.  Bullion  precipitation 
by  means  of  zinc  is  not  free  from  objections;  its  practice  is  connectetl 
with  a  loss  of  cyanide  and  with  the  introduction  into  the  process  of  a 
new  compound  (the  double  zinc-potassium  cyanide),  which  is,  to  say  the 
least,  not  an  advantage;  the  consumption  of  precipitating  agent  (zinc) 
is  far  in  excess  of  the  amount  theoretically  required,  and  no  opportunity 
is  offered  for  a  regeneration  of  the  cyanide.  The  precipitation  itself  is, 
however,  a  very  efficient  and  simple  procedure,  not  requiring  either 
motive  power  or  more  than  ordinary  attention,  and  the  treatment  of  the 


38  THE    CYANIDE    PROCESS. 

precipitates  cannot  be  said  to  offer  any  obstacles  which  would  charac- 
terize the  process  as  metallurgically  inefficient.  In  fact,  generally  speak- 
ing, the  clean-up  of  the  bullion  precipitated  by  zinc,  if  properly  handled 
on  the  lines  explained  above,  will  hardly  be  found  more  troublesome 
than  a  mill  clean-up. 

Although  the  precipitation  of  the  gold  by  zinc  is  unquestionably  a 
weak  point  in  the  cyanide  process,  no  other  method  has  as  yet  taken  its 
place  to  any  extent.  Had  other  methods,  which  require  motive  power, 
careful  adjustment  of  costly  and  delicate  machinery,  and  constant 
attention  preceded  it,  its  discovery  would  probably  have  been  con- 
sidered an  improvement  of  importance. 

(b)  The  MoUoy  Process. — A  method  for  precipitating  bullion  which 
has  obtained  some  technical  importance  has  been  advanced  by  B.  C.  Mol- 
loy,  of  Johannesburg,  whose  process  is  protected  by  English  letters 
patent  No.  3,024,  dated  16th  February,  1893.  Molloy  uses  for  precipita- 
tion purposes  sodium  or  potassium  amalgam,  which  is  formed  electro- 
lytically  from  a  solution  of  carbonate  in  contact  with  a  bath  of  mercury. 
The  alkali  metal  combines  with  the  cyanogen  of  the  gold  compound, 
forming  an  alkali  salt  of  the  cyanogen,  while  the  gold  is  instantly  amal- 
gamated. This  auriferous  amalgam  is  then  strained  and  melted  as 
in  an  amalgamation  mill.  The  process  of  precipitating  and  collecting 
the  bullion  is  carried  out  in  an  amalgamating  apparatus,  the  bottom  of 
which  is  partially  covered  with  mercury.  On  this  mercury  rests  the 
solution  from  which  the  metals  are  to  be  precipitated.  The  mercury  is 
charged  electrolytically  with  an  alkaline  metal  (by  the  electrolysis  of  an 
alkaline  salt  used  in  a  porous  vessel  in  contact  with  a  mercury  cathode). 
The  alkaline  metal,  or  its  amalgam,  when  coming  to  the  surface  of  the 
mercury  and  in  contact  with  the  water  of  the  solution,  decomposes  the 
water,  the  alkaline  metal  combining  with  the  oxygen  of  the  water  to 
form  an  alkaline  oxide;  the  hydrogen  of  the  decomposed  water  is  at  the 
same  time  evolved  in  a  nascent  state  from  the  surface  of  the  mercury 
which  is  in  contact  with  the  solution  from  which  the  gold  is  precipitated, 
and  absorbed  by  the  mercury.  The  gold  is  released,  from  the  mercury 
in  the  ordinary  manner  by  straining  and  distillation.  Another,  "  though 
much  less  advantageous  method,"  suggested  by  Molloy,  is  the  mechanical 
addition  to  the  mercury  of  potassium  or  other  alkaline  metals,  or  amal- 
gam of  the  same.  In  both  cases  the  original  solution  of  cyanide  of 
potassium  is  regenerated  and  ready  for  use  again.  The  reaction  is  aa 
follows: 

K.COg  +  elect,  current  =  Ko  +  CO2  +  0. 

KAuCya  -f  K  =  Au  -f  2  KCy. 

No  information  could  be  gained  of  the  actual  working  results. 
Other  methods  of  bullion  precipitation  by  means  of  the  electric  cur- 
rent have  been  suggested. 

(c)  The  Siemens  and  Halske  Process  for  bullion  precipitation 
by  electrolysis  on  lead  sheets  has  become  of  technical  importance.  The 
precipitation  plant  consists  in  boxes  through  which  the  gold  solution 
passes;  these  contain  the  anodes,  Avhich  are  iron  plates,  and  the  cathodes, 
which  are  lead  sheets,  stretched  between  iron  wires  fixed  in  a  light 
wooden  frame,  which  is  suspended  between  the  iron  plates.    It  is  claimed 


DEMONSTRATION    OF   PROCESS — METHODS   OF   OPERATION.  39 

that  the  adoption  of  this  method  of  bullion  precipitation  permits  the  use 
of  very  weak  cyanide  solutions  for  extracting  purposes,  followed  by  a 
•considerable  reduction  in  the  cost  of  treatment. 

Mr.  A.  von  Gernet  has  given  the  following  details  as  to  the  practical 
working  results  obtained  at  the  Worcester  works,  in  Johannesburg,  with 
the  Siemens  and  Halske  process,  which  has  been  tried  there  for  four 
months  on  a  large  scale,  after  long  and  exhaustive  preliminary  experi- 
ments at  the  works  of  the  Rand  Central  Ore-Reduction  Company: 

"  There  are  now  in  use  five  leaching  vats  of  2  ft.  in  diameter  with  10  ft. 
staves,  each  holding  2,700  cub.  ft.  One  tank  is  discharged  and  filled 
every  day.  The  strong  solution  used  contains  from  0.05  to  0.08  per  cent 
cyanide,  and  the  weak  washes  0.01  per  cent.  The  actual  extraction  of 
fine  gold  has  averaged  70  per  cent,  while  the  consumption  of  cyanide 
has  been  ^  lb.  per  ton  of  tailings  treated. 

"The  precipitation  plant  consists  of  four  boxes  20x8x4  ft.  Copper 
wires  are  fixed  along  the  top  of  the  sides  of  the  boxes,  and  convey  the 
current  from  the  dynamos  to  the  electrodes.  The  anodes  are  iron  plates 
7  ft.  long,  3  ft.  wide,  and  ^  in.  thick.  They  stand  on  wooden  strips 
placed  on  the  bottom  of  the  box,  and  are  kept  in  vertical  position  by 
Avooden  strips  fixed  to  its  sides.  In  order  to  effect  circulation  in 
solutions  passing  through  the  box,  some  of  the  iron  sheets  rest  on 
the  bottom,  while  others  are  raised  about  1  in.  above  the  level  of  the 
solution,  thus  forming  a  series  of  compartments  similar  to  those  of  a 
zinc  box,  the  difference  being  that  the  solution  passes  alternately  up  and 
down  through  successive  compartments.  The  sheets  are  covered  with 
canvas  to  prevent  short  circuit.  The  lead  sheets  are  stretched  between 
two  iron  wires,  fixed  in  a  light  wooden  frame,  which  is  then  suspended 
between  the  iron  plates.  The  boxes  are  kept  locked,  being  opened  once 
a  month  for  the  purpose  of  the  '  clean-up,'  which  is  carried  out  in  the 
following  manner:  The  frames  carrying  the  lead  cathodes  are  taken  out 
one  at  a  time.  The  lead  is  removed  and  replaced  by  a  fresh  sheet,  and 
the  frames  returned  to  the  box,  the  whole  operation  taking  but  a  few 
minutes  for  each  frame.  By  this  means  the  ordinary  working  is  not 
interrupted  at  all,  and  the  cleaning  out  of  the  boxes,  which  is  necessary 
in  the  zinc  process,  is  only  required  at  very  long  intervals.  The  lead, 
which  contains  from  2  to  12  per  cent  of  gold,  is  then  melted  into  bars 
and  cupelled.  The  consumption  of  lead  is  750  lbs.  per  month,  equal  to 
3  cents  per  ton  of  tailings.  The  working  expenses,  including  filling  and 
discharging  tanks,  come  to  80  cents  per  ton,  which  is  divided  as  follows: 
Filling  and  discharging,  20  cents  per  ton;  cyanide,  12^  cents;  lime,  2.4 
<;ents;  iron,  4.4  cents;  caustic  soda,  10  cents;  lead,  2.2  cents;  natives' 
wages  and  food,  3.8  centos;  coal,  9.2  cents;  white  labor,  9.2  cents;  stores 
and  general  charges,  6.5  cents;  total,  80  cents.  At  the  "Worcester  works 
100  tons  are  being  treated  per  day;  when  working  on  a  large  scale  it  is 
iinticipated  that  the  expenses  will  be  further  reduced."  (The  Mining 
Journal  of  London,  October  27,  1894.) 

The  advantages  claimed  for  this  process  are  that  electrical  precii)ita- 
tion  is  independent  of  the  amount  of  cyanide  or  caustic  soda  contained 
in  the  solution,  therefore  in  the  treatment  of  tailings  very  dilute  solu- 
tions can  be  used;  for  generating  the  current  necessary  in  a  3,000-ton 
plant,  2,400  Watts  are  required,  equal,  theoretically,  to  3}  horse-power, 
and  actually  requiring  about  5  indicated  horse-power.  The  process  has 
produced  755  ozs.  of  gold  during  the  month  of  July  of  this  year. 


a 


,nd 


40  THE    CYANIDE   PROCESS. 

(d)  The  Pielsticker  Process  applies  likewise  the  electric  current 
as  the  precipitating  agent.  A  description  of  this  process,  illustrated  hy 
a  diagram,  will  be  found  in  the  patent-specification  (see  Appendix). 
No  information  in  reference  to  practical  results  could  be  obtained.  The 
process  attained  of  late  a  certain  notoriety  on  account  of  the  patent 
litigation  now  pending  between  the  owners  of  the  MacArthur-Forrest 
patent  and  the  Cyanide  Gold  Recovery  Syndicate  (Limited)  of  London^ 
who  control  the  Pielsticker  patent. 

(e)  The  Moldenhauer  Process  of  bullion  precipitation  consists  in 
the  application  of  aluminium,  or  alloys,  or  amalgam  thereof,  in  the  pres- 
ence of  a  free  alkali.  It  is  claimed  that  aluminium  separates  the  gold 
very  quickly  from  the  cyanogen  solution  without  entering  into  combina- 
tion -with  the  cyanogen,  but  simply  reacting  with  the  caustic  alkali 
which  is  present  at  the  same  time,  forming  therewith  an  aluminate. 
The  precipitation  of  gold  by  aluminium  takes  place  as  follows: 

6  AuK  (CN)2  +  6  KHO  +  2  Al  -f  3  HoO  = 

6  Au  +  6  KCN  +  6  HCN  +  6  KHO  +  AlgOg 

6  Au  +  6  KCN  +  6  HCN  +  6  KOH  +  Al203= 

6  Au  +  12  KCN  +  6  H.O  +  AlgOg. 

The  whole  of  the  cyanide  of  potassium  which  has  been  combined  with 
the  gold  is  being  regenerated,  and  the  consumption  of  the  cyanide  is 
limited  to  the  loss  involved  by  such  secondary  reactions  as  act  decom- 
posing. (See  "chemistry  of  the  process.")  The  discoverer  of  this  method 
of  bullion  precipitation  claims  that  the  quantity  of  aluminium  required 
for  precipitating  the  same  quantity  of  precious  metal,  is  about  four  times 
less  than  the  amount  of  zinc  required  to  produce  the  same  effect.  No 
results  of  this  process  applied  on  a  large  scale  have  as  yet  been  made 
public. 

(f )  The  Johnston  Process  of  abstracting  gold  and  silver  from  their 
solutions  of  alkaline  cyanide  (United  States  patent  522,260,  see  Appen- 
dix) consists  in  the  use  of  pulverized  carbon,  preferably  in  the  form 
of  charcoal.  "The  pulverized  carbon  is  placed  upon  suitable  sup- 
ports so  as  to  form  it  into  filters,  through  a  series  of  which  the  cyanide 
liquid  is  caused  to  pass  successively,  leaving  the  metal  deposited  upon 
the  carbon.  The  gold  and  silver  are  then  recovered  by  carefully  burning 
the  carbon  and  smelting  the  residue  with  the  usual  fluxes.  By  thus 
employing  a  series  of  filters,  through  which  the  solution  is  passed  suc- 
cessively, 95  per  cent  of  the  precious  metal  contained  in  the  solution  is 
recovered.  When  only  one  filter  is  employed,  only  about  one  fourth  of 
the  gold  can  be  extracted." 

V.     PERCENTAGE  OF  EXTRACTION. 

The  percentage  of  extraction  depends  on  the  character  of  the  ore.  As 
I  mentioned  before,  the  process  is  suitable  for  many  ores  which  for 
chemical  and  mechanical  reasons  are  refractory.  The  commercial  ques- 
tion in  the  selection  of  a  metallurgical  process  for  treatment  of  a  certain 


jcr    cciii/   ui 


^„„-   ...   biic  guiu,  iii&teuu  ui  oo  pur  cent  us  snown  oy  assay;  ine 

returns  of  the  second  month  yielded  80  per  cent,  instead  of  91  per  cent; 
after  the  third  month  the  actual  results  came  up  to  the  extraction,  as  per 
assay — 89  per  cent.  Similar  experiences  have  been  made  in  the  Sylvia 
Company  in  New  Zealand  and  elsewhere.     It  has  been  recommended  to 


TABLE  SHOWING  RESULTS  OF  CYANIDE  TREATMENT  OF  ORES. 


Material. 

Operator. 

Assay  per  Ton. 

Value  per  Ton. 

Value. 

Percentage 
Extracted. 

Cost  of 

Name  of  Mioe. 

Character. 

Quantity 
Treated. 

Gold. 

silver. 

Gold. 

Silver. 

In  Ore 
Parcel. 

Extract 
from  Ore 
Parcel. 

Gold. 

Silver. 

per  Ton. 

Tons. 
5 

0.5 

280 

224 

30 

145 

16.9 

5 

11 

9.3 

90 

164 

206 

9 

5 

5 

1 

0.3 
0.5 
9.5 
10.5 
21 
37.9 
5 
1 
263.3 
43.1 
72.7 
192 
614 
0.6 
5 
7 

7.6 
0.9 
1 
1 
I 
111 
75 
0.9 
138 
19 
1 
116 
111 
130 
166 
422 
1,015 
4.5 
5 

4.5 
4.2 
3 

6.8 
116 
14.1 
4.1 
1.5 
13.3 
4.5 
17.5 
4.5 
1,600 
10.9 
12.6 
1.6 
7.1 
7.2 
14 
5.7 
1,000 
2.6 
1.5 
78 
5.2 
4.6 
5 

P.McIntyre 

07..  dwt.  gr. 
1    10    16 

...  8  4 
1  6  2 
1  2  20 
1  2  20 
1      2      1 

1  18     10 
3    15      0 

2  14      0 

3  0      0 

15  8 
7      5      7 

1  6    23 

2  11    10 

2  8      4 

1  6    12 

3  6    23 

3  16      0 

4  3      7 

3  17    22 

2  6      0 

4  2      0 

1  10      0 

2  8      4 

2  19    21 
1    12      0 

148    15      8 
222      7    12 
324      8    10 

'"3    '6    2.3 

16  3 
1      6      3 
1      7    18 

3  10    15 
1    16    22 

102      4      6 
123      4    11 

"b   "e  i2 

oz.  dwt.  gr. 

22    16    18 
3    15      0 
308    12    20 
488      3      6 
504      2    18 

'2S    ie    13 
19      0    14 

17  4    16 

18  0    23 
2    19      8 
1      1      6 

47      0    22 
52      9      6 

""6    "6    i7 

84,1 
90.0 
86.3 
81.8 
91.1 
822 
90.7 
91.3 
87.0 
87.2 
88.0 
88.0 
85.1 
91.2 
90.3 
89.3 
80.3 
lOO 
96 
88 
85.5 
87.7 
83.3 
86.0 
91.09 
90.6 
93 
93 
93 
94 

90.29 
81.18 
84.37 
80.78 
90.20 
86.31 
97.90 
97.20 
86.11 
86.34 
88.70 
80.32 
77.90 
89.10 
91 
89 
91 
91.6 
91.8 
91.8 
79.4 
82 
82 
9.S 
90 
80.2 
71.77 

"""98'"'" 
90.3 
90 
98 
84 
96 

"m"" 

97 

"rob"" 

90 
70 
94 

2 

clacK  jacK,  A         AuDtraifa' 

Slimes 

P.McIntyre 

P.McIntyre.. 

Day  Dawn,  Block  &  Windham,  Australia... 
Day  Dawn,  Block  &  Windham,  Australia... 
Day  Dawn,  Block  &. Windham,  Australia.. 
Day  Dawn,  Block  &  Windham,  Australia... 
Day  Dawn,  Block  &  Windham,  Australia... 

General  Grant,  Australia -.- 

Golden  Gate,  Australia 

4 

5 
6 

P.McIntyre....  

P.McIntyre.. 

8 
9 
10 
11 
12 
13 

P.McIntyre 

P.McIntyre. 

P.McIntyre 

Sludge.... 

Concentrates 

Mills  United,  Australia 

Mills  United,  Australia 

P.McIntyre 

15 

P.McIntyre 

1^ 

Mount  Morgan,  Australia 

Ore,  ironstone,  and  kaolin. 

19 

P.McIntyre 

New  Towers  Fxtend   Australia 

P.McIntyre. 

New  Towers  Extend.,  Australia 

P.McIntyre... 

•10 

New  Towers  Extend.,  Australia.. 

P.McIntyre.. 

Sludge 

Ore 

Ore 

Ore 

Alhurnia,  New  Zealand... 

Crown.New  Zealand 

56.78 
70.5 
79 
79 
79 
94 

79.78 
77.06 
83.70 
74,60 
16.10 
35.16 
100 
97.10 
67 
68.7 
59.58 
60 

64.45 
28.46 
61 
46.6 
49 
49 
49.8 
49.8 

""98"" 
98 
83 
61.65 

"s'g'gs 

63 

54.47 
3 
83 

$3  37 

MacConnell 

MacConnell 

Crown'  New  Zealand 

Ore                              .  . 

MacConnell 

$41,350  00 

3  50 

Kenilworth,  New  Zealand 

Kenilworth,  New  Zealand 

MacConnell 

Ore 

V 

Silverton,  New  Zealand 

Silverton,  New  Zealand 

Sylvia,  Tararu,  New  Zealand 

MacConnell 

. 

38 

39 
40 

Concentrates,  slimes 

Concentrates,  slimes 

A.  Scheidel 

A.  Scheidel.... 

A.  Scheidel 

A.  Scheidel. 

A.  Scheidel. 

1^  42,200  00 

Sylvia,  Tararu,  New  Zealand 

Sylvia,  Tararu,  New  Zealand 

Sylvia,  Tararu,  New  Zealand 

42 
43 
44 

Jigger  concentrates 

Coarse  concentrates 

4S 

Waihi,  New  Zealand 

Robert  Rose. 

Robert  Rose 

Robert  Rose 

Robert  Rose 

Robert  Rose 

Robert  Rose 

G.  &  8.  Extr.  Co.  of  Amer.. 

.1125  00 
22  50 
22  50 

22  60 

23  00 
23  00 

12  00 

13  00 
13  00 

6  00 
20  00 
10  80 

1.945  00 
1,705  00 
2,775  00 
3,010  00 
}  32,000  00 

42  87 
63  83 
60  57 

43  31 
113  74 

54'11 
2,920  00 
1,386  23 
63  20 
43  06 
198  50 
22  64 
220  60 
63  50 

52"86' 

166  42 
66  70 
253  68 
301  16 
487  20 
157  63 
«,0OO  00 
16  03 
56  24 
4,240  OO 
207  41 
10  08 
133  36 

2  25 

4li 

1  76 

47 

Ore 

1  50 

4K 

Waihi,  New  Zealand 

Waihi,  New  Zealand 

Waihi,  New  Zealand 

Boulder  City,  U.S.  A 

Boulder  City,  IT.  S.  A 

1  38 

4» 

Ore 

1  38 

hO 

138 

M 

$0  60 

60" 

44 

26  00 

1  04 

iei'is' 

11  IS 

2  46 
1  40 

3  51 

"i'he 

"""42 
1  49 
48  00 
39  00 
42  92 
63  00 

4  00 

pi  00 

66  65 
61  20 
44  20 

138  00 
69  26 

"'"'l'i546"49" 
79  97 
49  23 

233  07 
25  95 

262  60 

67  42 

6i"25" 

183  62 
67  50 
289  63 
340  17 
915  60 
170  50 

2  25 

W. 

2  60 

.W 

3  00 

M 

ChicagcU.  S.  A 

1  00 

55 

G.  &S.  Extr.  Co.of  Amer. 

3  00 

hH 

El  Capitan.  U.  S.  A.     . 

Eureka,  Cal„  D.  S.  A 

Flor  do  Marzo,  U.  S.  A 

Golden  CloudLD.  S.  A. 

Golden  Rose,  U,  S.  A 

Gregory,  U.  S.  A 

KingsOre,  U.  S.  A... 

ELematite 

Frue  concentrates  

1  13 

57 
5S 

A.  Scheidel 

3  60 
11  05 

51) 

8  40 

28  80 
16  00 

9  10 

15  00 
11  20 

""6 '20 
13  20 

"is '66" 
4  00 
2  40 

27  00 

10  40 
8  80 

38  00 

"39'26" 

16  40 

29  04 

2  50 

KO 

2  86 

til 

4  00 

m. 

3  00 

t)3 

Or5 

64 

McKeivie,  tj.  s.  A, :::::;".:'.;:::;:::;'.;:::".'.: 

Mercur,  Utah,  U.  S.  A 

Old  Charlie,  U.  S.  A. 

Siliciousore 

73 

""96"" 
33.6 
84 
87 
83.4 
62 
82 

2  25 

Ore 

Gill  S.Peyton 

2  40 

ti« 

1  50 

67 

Oro  Grande  U.  .S.  A 

311.  and  pyrites 

Ore  with  antimony 

G.  &  8.  Extr.  Co.  ol  Amer.. 
G.  &  8.  Extr.  Co.  of  Amer.. 
G.  &  S.  Extr.  Co.  of  Amer. 
G.  &S.  Extr.  Co.of  Amer.. 

1  21 

69 

Poorman,  U.  S.  A 

Poorman,  U.  S.  A.... 

Poorman,  U.  S.  A 

Poorman,  U.  S.  A 

Revenue,  U.  S.  A :"."."."': " 

Revenue,  U.  S.  A. 

R.  M,  Terror,  U.  S.  A. .; ::.\V.:\[:^[[[[ 

Rosecrance,  tJ.  8.  A 

Utica  Mine,  California,  U.  S.  A '.'.'.' 

Western  Belle,  U.  8.  A 

3  00 
500 

70 

6  83 

Stephanite 

Siliciousore 

6  49 

2  00 

V3 

Tailings 

F.  B.  &R.  B.Turner 

G.  &  S.  Extr.  Co.  of  Amer. 

74 

6  78 

3  75 

"'4 "92" 
2  24 

4  29 

36  63 
62  62 

"■"232'05 
83  88 
166  66 

88.6 

90 

93.18 

92 

88 

82.78 

75 

88 

"6"8;6"' 
48 
61.32 

2  50 

77 

Canvas  concentrates 

Silicions.. 

A.  Scheidel 

G.  &  8.  Extr.  Co.  of  Amer.. 

3  27 

4  40 

Wolferine.  U.S.  A.. 

Chicago,  Old  Mexico... 

600 

3re 

2  31 



PERCENTAGE    OF    EXTRACTION.  41 

ore  has  to  be  considered  parallel  with  the  chemical,  and  that  process 
should  be  adopted  which  permits  the  extraction  of  the  largest  percentage 
of  bullion  at  the  lowest  cost,  and  with  the  least  investment  of  capital. 
The  cyanide  process  is,  for  this  reason,  the  best  yet  discovered  for  the 
treatment  of  the  tailings  of  the  South  African  gold  fields,  although 
giving  only  an  average  of  extraction  of  about  70  per  cent,  of  which  about 
60  per  cent  is  recovered  (see  page  52).  No  other  process  gave,  at  the 
same  expenditure,  any  results  approaching  it.  The  conditions  of  the 
Witwatersrand  ores  are  considered  particularly  favorable  for  the  process, 
yet  the  extraction  figures  are,  in  most  instances,  not  high.  The  per- 
centage of  extraction  in  various  mills  in  Johannesburg  will  be  given  in 
the  chapter  on  the  process  in  Africa,  page  60.  The  ores  and  tailings  in 
New  Zealand,  where  cyanide  treatment  of  dry-crushed  ores  is  carried  on 
extensively,  give  better  results.  The  Waihi  ores,  pure  quartz,  the  gold 
free,  but  exceedingly  fine,  the  silver  in  form  of  sulphides,  no  sulphurets 
of  base  metals,  give  an  extraction  of  from  85  to  91  per  cent  of  the  gold 
assay-value,  the  silver  returns  varying  from  43  to  51  per  cent.  The  ore 
of  the  Crown  mines,  which  resembles  those  of  Waihi,  but  containing 
occasionally  telluride  of  gold,  yields  on  an  average  93  per  cent  of  gold 
and  79  per  cent  of  silver.  Concentrates,  if  satisfactory  at  all  in  cyanide 
treatment,  give  as  a  rule  very  high  figures.  A  considerable  quantity  of 
concentrates  from  the  Sylvia  Mine  in  New  Zealand,  of  a  very  complex 
character,  being  composed  chiefly  of  zinc-blende  and  copper  pyrites, 
with  a  large  percentage  of  galena  and  iron  pyrites,  were  treated  by  me 
by  cyanide,  and  gave  very  satisfactory  results  under  conditions  where 
no  other  means  of  treatment  were  at  disposal.  The  said  concentrates 
are  classified  by  the  dressing  plant;  the  fine  slimes  rich  in  bullion  and 
galena  gave  as  high  an  extraction  as  95.43  per  cent  of  the  gold  and 
86.69  per  cent  of  the  silver;  coarse  concentrates  gave  an  average  of  80.32 
per  cent  of  the  gold  and  50  per  cent  of  the  silver.  A  large  parcel  of  very 
fine  sulphurets  (from  the  canvas  plant)  from  the  Utica  Mine,  California, 
consisting  of  pure  iron  pyrites  in  finest  division,  mixed  with  more  or  less 
fine  sand  and  carbonate  of  lime,  proved  an  excellent  material  for  cyanide 
treatment;  the  extraction  averaged  93.18  per  cent  of  the  gold  value,  rising 
in  some  instances  as  high  as  96.57  per  cent.  The  coarse  concentrates  from 
the  Frue  vanners  did  not  give  such  good  results,  if  treated  direct;  their 
reduction  to  greater  fineness,  however,  improved  results.  An  appended 
table  shows  the  results  of  successful  treatment  of  parcels  of  ores  from 
various  sources.  It  is  to  be  regretted  that  no  corresponding  table,  giv- 
ing a  like  description  of  ores  treated  with  unsatisfactory  results,  can  be 
produced  for  comparison,  which  would  be  useful  and  instructive. 

The  recovery  of  the  bullion  should  correspond  with  the  extraction 
shown  by  assays;  in  practice,  however,  there  is  often  a  discrepancy,  which 
rnay  be  explained  by  various  causes;  new  vats,  particularly  those  of 
wood,  absorb  both  gold  and  cyanide,  and  considerable  differences  in  the 
returns  will  be  felt  during  the  first  weeks  of  their  use.  In  the  Waihi 
Company's  works  in  New  Zealand,  for  instance,  116  tons  of  ore,  of  an 
assay-value  of  about  -$25  per  ton,  returned  after  the  first  month  only  75 
per  cent  of  the  gold,  instead  of  85  per  cent  as  shown  by  assay;  the 
returns  of  the  second  month  yielded  80  per  cent,  instead  of  91  per  cent; 
after  the  third  month  the  actual  results  came  up  to  the  extraction,  as  per 
assay — 89  per  cent.  Similar  experiences  have  been  made  in  the  Sylvia 
Company  in  New  Zealand  and  elsewhere.     It  has  been  recommended  to 


40 

(c 
as  t] 
a  di: 
Noi 
proc 
litig 
pate 
who 

the; 
enc€ 
ver) 
tion 
whii 
The 


and 


T 
the 
limi 
posi 
ofb 
for  ' 
less 
resr 
pub 

solu 
dix 
of   ( 

pon 
liqu 
the 
the 
em  I 
cess 
recc 
the 


The  percentage  of  extraction  depends  on  the  character  of  the  ore.  As 
I  mentioned  before,  the  process  is  suitable  for  many  ores  which  for 
chemical  and  mechanical  reasons  are  refractory.  The  commercial  ques- 
tion in  the  selection  of  a  metallurgical  process  for  treatment  of  a  certain 


PERCENTAGE    OF    EXTKACTION.  41 

ore  has  to  be  considered  parallel  with  the  chemical,  and  that  process 
should  be  adopted  which  permits  the  extraction  of  the  largest  percentage 
of  bullion  at  the  lowest  cost,  and  with  the  least  investment  of  capital. 
The  cyanide  process  is,  for  this  reason,  the  best  yet  discovered  for  the 
treatment  of  the  tailings  of  the  South  African  gold  fields,  although 
giving  only  an  average  of  extraction  of  about  70  per  cent,  of  which  about 
60  per  cent  is  recovered  (see  page  52).  No  other  process  gave,  at  the 
same  expenditure,  any  results  approaching  it.  The  conditions  of  the 
Witwatersrand  ores  are  considered  particularly  favorable  for  the  process, 
yet  the  extraction  figures  are,  in  most  instances,  not  high.  The  per- 
centage of  extraction  in  various  mills  in  Johannesburg  will  be  given  in 
the  chapter  on  the  process  in  Africa,  page  60.  The  ores  and  tailings  in 
New  Zealand,  Avhere  cyanide  treatment  of  dry-crushed  ores  is  carried  on 
extensively,  give  better  results.  The  Waihi  ores,  pure  quartz,  the  gold 
free,  but  exceedingly  fine,  the  silver  in  form  of  sulphides,  no  sulphurets 
of  base  metals,  give  an  extraction  of  from  85  to  91  per  cent  of  the  gold 
assay-value,  the  silver  returns  varying  from  43  to  51  per  cent.  The  ore 
of  the  Crown  mines,  which  resembles  those  of  Waihi,  but  containing 
occasionally  telluride  of  gold,  yields  on  an  average  93  per  cent  of  gold 
and  79  per  cent  of  silver.  Concentrates,  if  satisfactory  at  all  in  cyanide 
treatment,  give  as  a  rule  very  high  figures.  A  considerable  quantity  of 
concentrates  from  the  Sylvia  Mine  in  New  Zealand,  of  a  very  complex 
character,  being  composed  chiefly  of  zinc-blende  and  copper  pyrites, 
with  a  large  percentage  of  galena  and  iron  pyrites,  were  treated  by  me 
by  cyanide,  and  gave  very  satisfactory  results  under  conditions  where 
no  other  means  of  treatment  were  at  disposal.  The  said  concentrates 
are  classified  by  the  dressing  plant;  the  fine  slimes  rich  in  bullion  and 
galena  gave  as  high  an  extraction  as  95.43  per  cent  of  the  gold  and 
86.69  per  cent  of  the  silver;  coarse  concentrates  gave  an  average  of  80.32 
per  cent  of  the  gold  and  50  per  cent  of  the  silver.  A  large  parcel  of  very 
fine  sulphurets  (from  the  canvas  plant)  from  the  Utica  Mine,  California, 
consisting  of  pure  iron  pyrites  in  finest  division,  mixed  with  more  or  less 
fine  sand  and  carbonate  of  lime,  proved  an  excellent  material  for  cyanide 
treatment;  the  extraction  averaged  93.18  per  cent  of  the  gold  value,  rising 
in  some  instances  as  high  as  96.57  per  cent.  The  coarse  concentrates  from 
tlie  Frue  vanners  did  not  give  such  good  results,  if  treated  direct;  their 
reduction  to  greater  fineness,  however,  improved  results.  An  appended 
table  shows  the  results  of  successful  treatment  of  parcels  of  ores  from 
various  sources.  It  is  to  be  regretted  that  no  corresponding  table,  giv- 
ing a  like  description  of  ores  treated  with  unsatisfactory  results,  can  be 
produced  for  comparison,  which  would  be  useful  and  instructive. 

The  recovery  of  the  bullion  should  correspond  with  the  extraction 
shown  by  assays;  in  practice,  however,  there  is  often  a  discrepancy,  which 
rnay  be  explained  by  various  causes;  new  vats,  particularly  those  of 
wood,  absorb  both  gold  and  cyanide,  and  considerable  differences  in  the 
returns  will  be  felt  during  the  first  weeks  of  their  use.  In  the  Waihi 
Company's  works  in  New  Zealand,  for  instance,  116  tons  of  ore,  of  an 
assay-value  of  about  .$25  per  ton,  returned  after  the  first  month  only  75 
per  cent  of  the  gold,  instead  of  85  per  cent  as  shown  by  assay;' the 
returns  of  the  second  month  yielded  80  per  cent,  instead  of  91  per  cent; 
after  the  third  month  the  actual  results  came  up  to  the  extraction,  as  per 
assay — 89  per  cent.  Similar  experiences  have  been  made  in  the  Sylvia 
Company  in  New  Zealand  and  elsewhere.     It  has  been  recommended  to 


42  THE    CYANIDE    PROCESS. 

soak  the  wooden  parts  of  a  new  cyanide  plant  with  paraffine  to  prevent 
absorption;  a  coat  of  asphalt  dissolved  in  bi-sulphide  of  carbon  will  be 
found  a  good  preventive  for  the  absorption  by  wood.  The  chief  sources 
of  chronic  losses  are  to  be  found  in  the  imperfect  separation  of  the  gold 
solution  from  the  exhausted  ore  residues,  and  in  the  faulty  methods  of 
dealing  with  the  bullion  after  its  precipitation  by  zinc.  There  is  no 
reason  why  the  actual  returns  should  differ  from  the  returns  as  estab- 
lished by  assay,  provided  all  mechanical  losses  are  prevented.  In  refer- 
ence to  the  losses  in  the  Johannesburg  mills,  see  chapter  on  the  process 
in  Africa,  page  52. 


VI.    WORKING  COSTS  OF  THE  PROCESS. 

As  may  be  deduced  from  the  whole  tenor  of  this  paper,  the  working 
costs  of  the  cyanide  process  vary  within  wide  limits  and  depend  on  many 
circumstances.  Locality  is  a  prime  factor  in  the  costs  of  working  any 
process,  and  expenses  must  be  high  where  operations  have  to  be  carried 
on  in  an  inaccessible  situation,  or  where  there  is  dearth  of  fuel,  water, 
building  material,  etc.  Apart  from  the  question  of  locality,  the  cost 
depends  principally  upon  three  factors: 

The  nature  of  the  ore. 

The  price  of  labor. 

The  price  of  cyanide. 

When  an  ore  contains  acid  salts  and  demands  an  alkali  treatment, 
the  price  of  the  alkali  must  necessarily  be  added  to  other  costs;  and 
where  the  ores  are  slimy,  recourse  must  be  had  to  drying  and  mixing 
appliances,  which  also  increase  the  cost  to  an  extent  depending  on  local 
■circumstances.  The  principal  labor  involved  in  the  process  is  the  charg- 
ing and  discharging  of  the  vats,  or,  if  agitation  is  used,  the  charging  of 
the  agitator  and  the  removing  of  the  exhausted  material  from  the  filter 
appliances.  The  charging  and  discharging  of  the  percolation  vats  may, 
under  ordinary  circumstances,  be  contracted  for  at  a  rate  of  about  25 
<jents  per  ton;  the  extent  of  the  operations  is  naturally  of  great  influence 
in  regulating  the  cost  of  handling.  Very  large  works  apply  mechanical 
means  for  discharging  the  vats,  such  as  dredges  and  movable  cranes, 
which  reduce  the  expense  of  labor  per  ton  of  ore  to  a  minimum.  To 
give  an  instance  of  the  labor  employed  in  working  the  agitation  process 
I  mention  the  Utica  works  in  California,  where  the  handling  of  the 
ore  and  all  the  labor  connected  with  the  treatment  amounts  to  $1  per 
ton;  this  applies  to  concentrates*varying  from  $50  to  $95  in  value  per 
ton.  The  cost  of  the  cyanide  is  one  of  the  principal  charges  in  the 
process,  and  the  cost  of  treatment  depends  to  a  great  extent  upon  the 
price  of  cyanide  and  on  the  amount  consumed  per  ton  of  ore.  The  price 
•of  cyanide  of  from  95  to  98  per  cent  strength  now  averages  about  50  cents 
per  pound,  delivered  at  seaports,  and  for  lower  strength  the  rates  are 
somewhat  better. 

The  amount  of  cyanide  consumed  per  ton  of  ore  is  between  1  lb.  and  3 
lbs.;  the  character  of  the  ore  has,  however,  the  greatest  influence  on  the 
consumption,  and  in  many  cases  the  cyanide  process  will  be  found  the  best, 
cheapest,  and  quickest  method,  even  if  a  considerably  larger  amount  of 
cyanide  is  consumed  per  ton.  Naturally,  as  the  quantity  treated  is  greater 
the  cost  becomes  proportionally  less.     In  some  mines,  as  at  the  Primrose 


WORKING   COSTS,    ETC.  43 

Company,  Johannesburg,  tailings  are  treated  for  about  $1  per  ton,  and  it 
is  very  seldom  that  the  cost  in  the  Transvaal  exceeds  $2  50.  In  the 
Crown  Reef  works  the  cost  of  treatment  ranges  from  $1  to  $1  37  per 
ton;  this  includes  the  royalty,  which  for  the  use  of  the  MacArthur-Forrest 
patents  amounts  in  South  Africa  to  $1  25  per  standard  ounce  of  gold. 
In  Revenue,  Montana,  the  cost  of  treatment  per  ton  of  ore,  including 
crushing,  amalgamating,  cyanide  treatment,  and  royalty  of  •$!  per  ton, 
amounts  to  from  $4  to  $5  per  ton.  The  cost  of  treatment  of  ore  at  the 
Mercur  Mine,  Utah,  amounts  to  $2  40  per  ton,  not  including  royalt}'. 
The  cost  of  ore  treatment  in  the  Crown  mines.  New  Zealand,  is  from 
$3  37  to  $3  50;  in  the  Waihi  Company's  works.  New  Zealand,  the  cost 
amounted  to  $2  25  per  ton  of  ore;  the  expenses  are  now  reduced  to 
$1  25,  cost  of  crushing  and  patent-royalty  of  7^  per  cent  on  the  bullion 
value  not  included.  The  treatment  of  concentrates  is,  as  a  rule,  more 
expensive  than  that  of  ore  and  tailings;  their  value  is,  however,  in  most 
cases,  considerably  higher  than  that  of  those  materials,  so  that  the  cost 
per  ounce  of  gold  extracted  is,  with  concentrates,  generally  much  lower 
than  with  ore  and  tailings.  The  agitation  treatment  of  concentrates 
(sulphurets)  costs  in  the  Utica  works,  California,  from  $3  25  to  $3  50 
per  ton,  labor  included.  "  Ores  yielding  upwards  of  90  per  cent  of  their 
gold  assay-value  have  been  treated  at  $1  25  per  ton,  and  tailings  con- 
taining less  than  $3  have  been  worked  profitably.  It  is  therefore  safe 
to  assume  that  under  favorable  circumstances,  and  apart  from  all  costs 
of  mining  and  crushing,  the  cyanide  process  is  capable  of  application  at 
a  low  figure." 

VII.     COST   OF   CYANIDE    PLANTS. 

The  cost  of  cyanide  plants  varies  naturally  with  the  system  applied 
and  the  extent  of  the  works.  A  well-equipped  plant  with  a  capacity  of 
50  tons  per  day  will  cost  about  $25,000,  a  100-ton  plant  about  $40,000. 
I  shall  have  occasion  to  give  details  on  the  cost  of  plants  when  describ- 
ing prominent  and  successful  plants  in  different  parts  of  the  world,  and 
I  refer  particularly  to  the  corresponding  chapter  of  the  process  in  Africa, 
page  55. 

VIII.     MACHINERY  AND  APPLIANCES. 

In  discussing  the  various  methods  of  applying  cyanide,  the  ma- 
<:hinery  for  each  purpose  has  been  described  (see  Chapter  IV).  Gen- 
erally speaking,  all  plants  have  the  same  main  features;  modifications, 
however,  will  be  suggested  by  special  conditions  of  locality  and  char- 
acter of  ore.  Economy  in  handling  the  ore  is  of  the  greatest  impor- 
tance, and  should  be  made  of  first  consideration  in  selecting  the  site 
for  the  plant  and  in  its  arrangement.  The  crushing  machinery,  if  ores 
are  to  be  treated  without  previous  amalgamation,  should  be  selected  in 
accordance  with  the  character  of  the  material.  The  proper  prejjaration 
of  the  ore  is  a  very  important  item,  and  the  crushing  machinery  should 
be  selected  so  as  to  produce  the  smallest  amount  of  dust  if  dry-crushing 
and  of  slimes  if  wet-crushing  of  the  ore  is  practiced.  For  drv-crushing, 
rolls  should  be  preferred,  on  account  of  their  giving  a  product  of  greater 
uniformity  than  stamps,  which  are  now  used  to  a  great  extent.  It  is 
with  the  cyanide  process  as  with  other  leaching  processes,  the  more 


44  THE    CYANIDE    PROCESS. 

equal  in  size  the  particles  are,  the  better.  Wet-crushing,  with  the 
improvements  necessary  for  mastering  the  slime  difficulty,  may  ulti- 
mately win.  Pumps  of  all  constructions  may  be  used  for  the  transporta- 
tion of  the  solutions,  provided  their  material  is  not  attacked  by  the 
alkaline  cyanide  solution.  I  shall  refer  to  the  general  arrangement  of 
plants  in  the  corresponding  chapter  of  the  process  in  Africa,  page  55. 


IX.     LABORATORY  WORK. 

Exact  laboratory  experiments  must  precede  all  cyanide  mill  opera- 
tions; the  required  fineness  of  the  ore,  the  strength  of  the  cyanide 
solution,  and  the  length  of  time  for  its  action  on  the  ore,  have  to  be 
established  by  experiment.  The  correct  strength  necessary  for  treating 
any  class  of  ore  may  be  readily  determined  in  the  laboratory  by  treating 
a  weighed  quantity  of  the  ore  with  cyanide  solutions  of  different  strength 
and  for  various  periods  of  time.  After  treatment,  the  amount  of  gold 
extracted  and  the  quantity  of  cyanide  consumed  should  be  determined. 
These  results  are  then  compared  with  the  original  contents  of  gold  and 
silver  in  the  ores  and  the  original  strength  of  cyanogen  in  the  solution 
used.  A  method  of  rapidly  determining  the  gold  in  the  cyanide  liquors 
consists  in  evaporating  a  known  quantity  to  dryness  on  lead  foil  (free  of 
■silver),  and  cupelling  the  lead  in  the  usual  manner.  In  the  presence  of 
base  metals,  the  liquor  should  be  evaporated  with  the  addition  of  litharge, 
and  the  residue  assayed  for  gold  and  silver  in  the  usual  manner.  Tlie 
point  to  be  aimed  at  is  to  consume  as  little  as  possible  of  cyanide  and  to 
extract  at  the  same  time  as  high  a  percentage  of  gold  and  silver  as  pos- 
sible. The  water  used  for  making  up  the  solutions  should  be  examined 
for  carbonic  acid,  free  sulphuric  acid,  and  sulphates.  A  chief  point  to 
be  investigated  in  the  laboratory  is  the  "  acidity  "  of  the  ore,  by  which 
term  is  understood  the  presence  of  products  arising  from  the  decompo- 
sition of  sulphurets.  These  chiefly  consist  of  free  sulphuric  acid  and  of 
products  derived  from  a  more  or  less  advanced  oxidation  of  pyritic 
matter,  such  as  proto-  and  per-sulphates  and  basic  iron  salts.  The  exact 
amount  of  free  acid  contained  in  an  ore  sample  can  be  readily  deter- 
mined by  shaking  a  certain  weight  with  water,  and  adding  standard 
normal  or  one-tenth  normal  caustic  soda  solution,  till  the  point  of  alka- 
linity is  reached,  as  indicated  by  litmus  or  some  other  indicator.  The 
means  to  prevent  the  ill  effects  of  acidity  have  been  discussed  in  the 
chapter  on  chemistry.  The  amount  of  soda  or  lime  required  for  the  ore 
is  easily  calculated  from  the  consumption  of  normal  soda  solution  as 
shown  by  the  above  experiment.  The  cyanide  solution  will  in  many  cases 
contain  after  the  treatment  of  ore  the  evidence  of  secondary  reactions,  and  a 
complete  chemical  analysis  of  the  solution,  before  it  comes  into  contact  with 
the  zinc,  should  in  all  cases  he  made.  The  explanation  of  ^m satisfactory 
results  with  cyanide  treatment  will  be  found  in  many  instances  by  means  of 
such  an  examination. 

The  reasons  why  one  ore  yields  its  gold  readily  to  cyanide  treatment, 
and  others  of  a  similar  chemical  composition  do  not,  are  not  always 
apparent;  chemical  analysis  and  microscopical  examination  should  be 
used  along  with  practical  tests.  As  a  programme  for  the  examination  of 
an  ore  in  reference  to  its  fitness  for  cyanide  treatment,  the  following  may 
be  suggested:    (1)  The  ore  shall  be  crushed  and  passed  through  a  30-mesh 


LABORATORY    WORK DANGER    IN    WORKING.  45 

sieve,  and  part  of  it  assayed.  (2)  The  "acidity,"  if  any,  of  the  ore, 
shall  be  determined,  as  described  before,  in  say  100  grams;  if  necessary, 
water  and  alkali  washes  will  then  be  applied  before  the  ore  is  submitted 
to  cyanide  treatment.  (3)  Shaking  tests  in  glass  bottles  with  solutions 
of  various  strength  during  various  periods  of  time  will  determine  the 
amount  of  cyanide  consumed  by  the  ore,  the  strength  of  solution  required, 
and  the  time  necessary  for  the  reaction.  Cyanide  determination  in  the 
solution  and  assay  of  the  ore,  after  treatment,  provide  the  required  data. 
Agitation  tests  will  decide  if  an  ore  is  suited  for  cyanide  or  not.  In 
cases  of  successful  cyanide  treatment  by  shaking  tests,  percolation  tests 
of  samples  should  then  be  made.  The  simplest  apparatus  for  the  pur- 
pose is  a  glass  funnel  of  large  size,  the  neck  of  which  is  closed  by  an 
india-rubber  pipe  and  clip;  a  lamp  chimney  closed  at  one  end  by  a 
stopper  of  india-rubber,  which  carries  a  glass  tube,  may  be  used  for 
the  same  purpose.  The  ore  is  placed  on  a  filter-bed  of  pebbles,  which 
is  covered  by  a  piece  of  flannel  or  filter-paper.  Experiments  with  equal 
weights  of  ore,  but  with  solutions  of  various  strength,  and  exposed  dur- 
ing various  periods  of  time,  should  be  made  simultaneously;  analyses 
of  the  percolated  solutions  and  assays  of  the  well-washed  residues  will 
then  show  the  best  conditions  of  treatment.  Small  tests,  if  properly 
conducted,  are  excellent  guides  as  to  the  treatment  of  ore  on  a  large 
scale.  In  a  cyanide  plant  there  is  ample  employment  for  the  chemist  in 
charge;  all  operations  should  be  controlled  by  him  by  assays  and 
analyses;  improvements  on  all  parts  of  the  process  may  be  effected  by 
careful  observation  and  continued  investigation.  The  non-success  of 
the  cyanide  process  in  various  mining  camps  may  be  attributed  to  the 
incompetency  of  the  men  to  whose  care  the  works  were  intrusted. 
Mine  owners  will  find- it  profitable  to  employ,  at  least  during  the  first 
time  of  their  using  cyanide,  a  competent  man,  instead  of  "finding  out" 
for  themselves  at  the  expense  of  much  time  and  money.  When  the 
process  is  once  successfully  and  firmly  established,  an  intelligent  fore- 
man will  easily  acquire  the  necessary  knowledge  to  test  and  make  up 
the  solutions. 


X.     DANGER  IN  WORKING  THE  PROCESS. 

The  deadly  poisonous  character  of  the  reagent  was  once  considered  to 
be  a  great  obstacle  in  the  way  of  its  successful  introduction.  However, 
in  the  first  place,  the  solutions  used  are  so  diluted  that  the  hydrocyanic 
acid  evolved  from  them  is  of  no  consequence  if  the  works  are  properly 
ventilated.  For  safety,  as  much  as  for  practical  reasons,  all  materials 
should  be  tested  for  acid  before  treatment,  and,  if  necessary,  neutralized. 
In  the  second  place,  there  is  no  necessity  for  those  working  the  process 
to  come  into  contact  with  cyanide,  solid  or  in  solution;  even  properly 
conducted  cleaning  up  does  not  require  contact.  Some,  but  very  few, 
have  a  susceptibility  for  cyanide,  and  with  them  the  most  diluted  solu- 
tions, if  brought  into  contact  with  the  skin,  produce  eruptions,  which, 
although  not  dangerous,  are  itching  and  annoying;  such  men  should 
not  be  employed  in  cyanide  works.  In  case  of  bad  ventilation,  com- 
plaints of  headache,  faintness,  and  dizziness  may  be  heard.  In  instances 
where  circumstances  require  that  hands  and  arms  should  be  brought  in 
contact  with  the  solution,  I  found  a  coating  of  oil  or  coal  oil  (kerosene) 


46  THE    CYANIDE    PROCESS. 

an  eftective  protection  for  the  skin.  The  process  is  now  used  so  generally^ 
and  on  such  a  gigantic  scale,  that  many  hundred  men  are  constantly 
employed  in  the  works;  considering  the  dangerous  character  of  the 
cyanide,  the  number  of  accidents  is  remarkably  small,  and  it  may 
justly  be  said  that  no  more  danger  is  incurred  in  the  working  of  the 
cyanide  process,  under  ordinary  precautions,  than  there  is  in  working 
in  establishments  of  chemical  and  metallurgical  industries,  where  corro- 
sive liquids  and  acids  are  constantly  in  use.  Extraction  of  gold  and 
silver  by  cyanide  will  compare,  as  to  fatal  accidents,  very  favorably  with 
most  chemical  and  metallurgical  industries.  It  is,  however,  always  well 
to  instruct  the  men  how  to  act  in  cases  of  emergency:  Put  the  patient  into 
a  hot  bath  and  apply  cold  water  to  his  head  and  back.  In  cases  of  inter- 
nal poisoning,  vomiting  by  physical  means,  or  by  emetics,  is  advised. 
Freshly  precipitated  carbonate  of  iron,  obtained  by  mixing  equal  quan- 
tities of  sodium  carbonate  and  ferrous  sulphate,  is  recommended  for 
internal  use;  the  two  chemicals  should  be  kept  on  hand  ready  for  com- 
pounding this  antidote.  If  the  poisoning  is  the  consequence  of  inhala- 
tion of  hydrocyanic  acid,  it  is  advisable  to  make  the  patient  inhale  a 
small  quantity  of  chlorine  gas,  ammonia,  or  ether;  rubbing  with  cam- 
phor-alcohol is  recommended.  It  has  been  reported  of  late  that  Dr. 
Johann  Antal,  a  Hungarian  toxicologist,  has  notified  the  Hungarian 
Society  of  Medicine  that  he  had  found  a  perfect  antidote  for  prussic 
acid  in  nitrate  of  cobalt;  he  quoted  forty  cases  of  its  use  with  perfect 
success. 


XI.    EXEMPLIFICATION   OF   THE   PROCESS— THE  PROCESS 
IN  VARIOUS   COUNTRIES. 

After  having  given  the  outlines  of  the  process,  and  the  various  methods 
of  its  use,  I  now  propose  to  describe  its  practical  application  in  different 
parts  of  the  world. 

A.    The  Process  in  Africa. 

The  cyanide  process  has  found  its  earliest  application  on  a  large  ecale- 
in  the  Witwatersrand  gold  fields  of  Johannesburg,  South  African  Re- 
public. The  use  of  the  process  has  since  been  extended  to  the  difi'erent 
gold  fields  of  the  republic,  the  output  of  which  has  gone  on  steadily 
increasing,  rather  by  application  of  improved  machinery  and  the  Mac- 
Arthur-Forrest  recovery  process,  than  by  the  opening  up  of  new  mines. 
In  the  following  notes,  describing  the  methods  of  cyanide  treatment  in 
South  Africa,  I  give  chiefly  the  general  information  obtained  from  Mr. 
J.  M.  Buckland,  the  General  Manager  of  the  African  Gold  Recovery 
Company  of  Johannesburg,  and  embody  in  them,  at  the  same  time,  the 
special  information  obtained  from  other  gentlemen  in  charge  of  promi- 
nent companies  and  works. 

The  Ores. — "At  the  Witwatersrand,  from  which  at  present  some  forty- 
five  thousand  ounces,  or  about  90  per  cent,  of  the  gold  obtained  in  South 
Africa  by  the  cyanide  process  is  obtained,  the  ore  nwy  be  classed  generally 
as  conglomerate,  locally  called  'banket'  (almond-rock).  This  consists 
practically  of  quartz  pebbles  embedded  in  a  quartzose  matrix,  which  last 
carries  the  gold  and  a  varying  proportion  of  iron  pyrites.  There  is  also  a 
small  quantity  of  alumina'in  most  'banket,'  existing  in  diverse  forms  of 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS    IN    AFRICA.  47 

corundum  and  (combined  with  silica)  of  clay.  The  latter  is  the  cause 
of  much  of  the  slimes  formed  during  the  crushing  process,  the  cheap  and 
profitable  treatment  of  which  by  cyanide  still  remains  a  difficult  problem. 
The  iron  pyrites  almost  invariably  contain  traces  of  copper  and  nickel 
as  sulpliides.  Within  50  to  100  ft.  of  the  surface,  the  'banket'  is 
more  or  less  weathered,  and  the  iron  exists  in  an  oxidized  form;  but 
below  this  depth  the  ore  becomes  paler  in  color,  less  friable,  and  conse- 
quently more  difficult  to  crush,  and  iron  pyrites  takes  the  place  of  the 
iron  oxide.  The  gold  also  is  more  difficult  of  extraction  by  amalgama- 
tion or  by  cyanide;  but  whether  in  this  latter  case  the  cause  is  chemical 
or  mechanical  is  not  yet  determined.  On  the  latter  hypothesis,  the 
difficulty  would  consist  in  the  fact  that  the  particles  of  gold  are  so 
imbedded  between  the  cleavage  planes  of  the  pyrites  as  to  prevent  to  a 
great  extent  contact  with  cyanide  solution;  and,  on  the  former,  that  the 
gold  exists  chemically  combined  with  certain  constituents  of  the  ore, 
such  as  sulphur  and  arsenic — the  cyanide  having  presumably  not  suffi- 
cient affinity  to  act  as  a  solvent  by  breaking  up  the  bond  of  union. 

"  At  the  Sheba  Mine,  De  Kaap  District,  the  ore  is  a  quartzite,  contain- 
ing a  small  amount  of  iron  pyrites  and  talc.  When  crushed,  there  are 
formed,  owing  to  weathering,  sulphates  of  iron  and  free  sulphuric  acid, 
which  react  on  the  talc  (silicate  of  magnesia),  forming  sulphate  of 
magnesia,  and  this  salt  may  be  observed  as  an  efflorescence  on  many 
of  the  tailings-dumps.  This  compound,  like  all  others  in  which 
the  '  base '  is  weaker  than  potash  and  the  '  acid '  stronger  than  hydro- 
cyanic acid,  causes  decomposition  and  loss  of  cyanide  (see  chapter 
on  chemistry).  At  the  Barrett  Company  (Kaapsche  Hoop),  the  ore  is 
a  very  soft,  decomposed  talcose  slate,  containing  a  large  proportion  of 
hydrated  iron  oxide.  Owing  to  the  very  fine  nature  of  the  gold  the 
solution  of  it  is  almost  complete,  but  sufficient  of  the  very  finely  divided 
portion  of  the  ore  passes  through  the  filter  cloth,  coats  the  zinc,  and 
prevents  thereby  the  gold  solution  from  coming  into  contact  with  it; 
precipitation  is  consequently  seriously  interfered  with.  The  difficulty 
in  such  cases  is  met  to  a  certain  extent  by  the  use  of  an  extra  vat, 
placed  between  the  leaching  vats  and  the  precipitating  boxes,  in  which 
the  greater  part  of  the  suspended  matter  is  allowed  to  settle,  and  tolera- 
bly clear  liquid  is  filtered  off.  This  ore  is  of  so  soft  a  nature  as  not  to 
require  any  explosives  in  mining;  it  does  not  even  require  preliminary 
crushing  for  the  purpose  of  preparing  it  for  treatment,  but  is  simply 
sifted  through  drums,  and  the  portion  which  passes  through  the  sieve, 
when  mixed  with  coarse  tailings  to  assist  filtration,  is  ready  for  cyanide 
treatment. 

Ore  Reduction. — "At  present,  with  the  above-mentioned  exception,  all 
ores  in  the  Transvaal  gold  fields,  which  are  treated  by  cyanide,  have 
previously  undergone  the  ordinary  crushing  and  amalgamation  process 
in  the  battery.  The  wet-crushing  stamp-mill  is  the  only  machine 
employed  for  ore  reduction,  apart  from  various  grinding  machines,  such 
as  the  Wheeler  and  Berdan  pans,  which  are  rarely  used  for  the  finer 
reduction  of  tailings  and  concentrates.  At  the  Rand  ( Witwatersrand), 
the  average  mesh  employed  for  battery  screens  is  thirty  holes  to  the 
linear  inch  (No.  30  screen),  or  900  to  the  square  inch.  In  some  cases, 
however,  No.  24  screens  are  used.  At  mines,  such  as  the  Sheba,  where 
the  gold  is  very  fine,  No.  40  screens  are  employed,  but  the  tonnage  per 
stamp  per  twenty-four  hours  is  in  such  cases  not  much  more  than  twa 


48  THE    CYANIDE    PKOCESS. 

tons,  as  compared  with  the  three  and  two  thirds  tons  usual  for  mills 
crushing  Rand  '  banket.' 

"  In  an  experimental  way,  a  solution  of  cyanide  has  been  used  instead 
of  battery  water;  at  present,  however,  water  is  invariably  used  in  the 
mortar  boxes,  sufficient  success  not  having  attended  the  other  method. 
The  use  of  cyanide  solution  in  the  mortars  would  be  of  advantage  only 
when  the  pulp  is  directly  delivered  into  the  percolation  vats;  the  for- 
mation of  slimes  is  fatal  to  this  method.  There  is  now  no  other  process 
than  the  cyanide  process  used  in  treatment  of  tailings,  and  no  mill  of 
which  the  tailings  are  of  sufficient  value  is  considered  complete  without 
a  cyanide  plant.  On  the  Witwatersrand  alone  there  are  upwards  of 
forty  cyanide  plants  in  operation,  and  ten  in  process  of  construction; 
the  present  quantity  of  tailings  treated  monthly  is  about  250,000  tons. 
On  the  other  gold  fields — DeKaap,  Lydenburg,  and  Klerksdorp — there 
are  in  all  ten  cyanide  plants  in  operation. 

Method  of  Applying  Cyanide. — "  The  method  of  applying  cyanide  to 
gold  extraction  is  that  specified  in  the  MacArthur-Forrest  patents,  of 
which  the  African  Gold  Recovery  Company  holds  the  rights  in  Africa, 
and  lets  out  the  right  of  using  the  process  to  gold-mining  companies  on 
royalty,  usually  10  per  cent  on  the  value  of  the  gold  produced.  Nearly 
all  companies  using  the  process  erect  and  work  their  own  plants,  paying 
royalty  as  above."     Some  custom-works  will  be  mentioned  later  on. 

The  mode  of  procedure  in  applying  the  cyanide  process  in  Africa  is 
generally  that  which  has  been  outlined  in  the  earlier  part  of  this  paper. 
Some  further  details,  however,  will  here  be  given  and  may  prove  of 
interest.     The  general  system  of  treatment  is  that  of  percolation  in  tanks. 

The  Vats. — "The  percolation  tanks,  or  leaching  vats,  vary  greatly  in 
size  and  shape.  Those  first  constructed  were  from  15  ft.  to  20  ft.  square, 
and  from  4  ft.  to  5  ft.  deep,  the  material  used  being  boards  9  in.  wide  by 
3  in.  thick  and  as  long  as  the  side  of  the  vat.  Owing  chiefly  to  the 
difficulty  of  making  these  water-tight,  oval  and  finally  round  vats,  com- 
posed of  staves  2^  in.  thick,  6  in.  wide,  and  varying  in  length  from  5  ft. 
6  in.  to  11  ft.,  were  used.  Vats  now  vary  in  diameter  from  15  ft.  to  40 
ft.,  and  in  capacity  from  30  to  600  tons.  The  employment  of  bottom 
discharge,  by  which  the  exhausted  tailings,  or  'residues,'  are  shoveled 
through  a  hole  in  the  bottom  directly  into  a  truck  below,  has  rendered 
the  great  increase  in  depth  possible.  '  Side  discharge '  through  doors  in 
the  side  of  the  vat  is  also  employed  to  some  extent.  Discharge  over  the 
side  into  trucks  on  tram-lines  is  now  used  only  in  cases  when  first  cost, 
or  '  want  of  fall,'  in  the  dumping-ground  is  a  serious  consideration.  The 
loading  into  trucks  does  not  cost  more  than  4  cents  per  ton,  even  under 
unfavorable  conditions,  and  is  only  2  cents  and  even  less  per  ton  in  some 
cases.  At  the  Barrett  Company,  the  residues  are  shoveled  through  an 
opening  in  the  bottom  of  the  vat  into  a  launder,  where  a  stream  of  water 
carries  them  away."  Some  companies,  like  Le  Champ  d'Or  French 
Gold  Mining  Company,  let  the  filling  and  emptying  of  their  cyanide 
tanks  by  contract. 

"In  some  of  the  largest  works  cement  vats  are  used,  particularly  for 
'  sumps,'  or  tanks,  where  the  solution  is  stored  after  passing  through 
the  precipitation  boxes.  Such  vats  are  really  excavations  lined  with 
bricks,  laid  in  hydraulic  mortar,  and  plastered  inside  with  cement; 
these  attain  a  capacity  of  600  tons,  being  50  ft.  in  diameter  and  9  to 
11  ft.  deep.     For  discharging  them,  when  they  are  used  as  percolation 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS    IN    AFRICA.  49 

vats,  either  tram-lines  are  laid  down  along  the  bottom,  passing  out 
through  doors,  which  are  bolted  and  made  water-tight  when  the  vat  is 
in  use,  or  else  trucks  are  lowered  by  a  steam  crane  into  the  vat,  and 
filled  by  natives,  and  again  hoisted"  (see  diagrams,  page  57).  "At  the 
Salisbury  works  a  tailings  wheel  lifts  the  pulp,  after  passing  over  the 
amalgamating  plates,  to  a  flume,  which  carries  it  to  a  hydraulic  sepa- 
rator, which  separates  the  slimes  from  the  coarse  tailings.  This  is  done  to 
render  the  subsequent  treatment  of  the  tailings  more  economical,  as  easy 
filtration  is  achieved  when  tailings  free  from  slimes  are  treated.  The 
slimes  are  treated  by  themselves  and  filtered  in  filter-presses.  Many 
companies  now  run  the  material  from  the  mill  into  intermediate  settling- 
vats,  provided  with  bottom  or  side  discharge,  for  convenience  of  loading 
the  trucks  which  transport  it  to  the  cyanide  works.  The  difficulty  of 
insuring  an  equal  mixture  of  fine  and  coarse  tailings  is  met  by  means 
-of  a  rotary  distributor,  pivoted  above  the  center  of  the  vat  and  discharg- 
ing into  it.  This  distributor  consists  of  pipes  of  different  lengths 
diverging  from  a  central  basin  into  which  the  pulp  is  delivered.  The 
openings  at  the  end  of  the  pipes  are  so  arranged  that  the  stream  of  pulp 
issuing  therefrom  causes  the  distributor  to  rotate."  In  the  Nigel  Com- 
pany's works  the  slimes  are  separated  from  the  sand  by  means  of  tailings- 
pits,  with  overflow  into  pits  where  the  slimes  are  collected;  these  are 
dried,  broken  up,  and  delivered,  mixed  with  the  clean  sand,  into  the 
vats  in  the  works. 

Treatment  of  Concentrates. — "  Concentrates  are  not  now  treated  by  agi- 
tation in  the  Witwatersrand  gold  fields;  percolation  has  been  substituted 
ior  it.  A  period  of  contact  and  percolation,  extending  from  two  to  four 
weeks,  is  now  usually  employed.  Agitation  has  been  abandoned  on 
account  of  its  cost,  consequent  upon  the  power  and  constant  attention 
required,  and  the  necessarily  small  amount  treated  at  one  time.  In 
addition,  it  was  found  that  the  cyanide  consumption  was  usually 
increased  by  the  solution  becoming  heated,  owing  to  the  friction  of  the 
solid  particles  during  an  agitation  of  several  hours.  In  treating  by 
ordinary  percolation,  the  concentrates  are  usually  mixed  with  a  suffi- 
cient amount  of  coarse  tailings  to  insure  filtration.  Transferring  the 
material  from  one  vat  to  another  at  intervals  of  a  few  days  is  sometimes 
oonsidered  beneficial,  for  the  purpose  of  obtaining  a  supply  of  oxygen 
as  required  by  Eisner's  equation."    (See  chapter  on  chemistry,  p.  16.) 

"Although  pyrites  themselves  consume  practically  no  cyanide,  the 
great  difficulty  incurred  in  the  treatment  of  concentrates  generally,  and 
of  some  tailings,  is  due  to  the  fact  of  their  having  been  partially  oxidized 
by  exposure  to  the  air."  The  reactions  thereby  taking  place  have 
already  been  mentioned  as  detrimental  in  the  chapter  on  chemistry, 
and  the  remedies  enumerated  (see  p.  18).  "The  water-washings  em- 
ployed to  remove  the  'acidity,'  as  it  is  termed,  take  place  in  a  special 
vat,  as  the  traces  of  the  cyanide  retained  by  the  filter-cloth,  etc.,  of  the 
regular  leaching  vat  are  liable  to  dissolve  gold,  and  thus  cause  loss. 
Experiments  have  shown  that  a  water-wash  pure  and  simple  will  dis- 
solve out  of  most  tailings  a  minute  quantity  of  gold,  but  this  is  so  small 
an  amount  that  it  may  be  neglected.  If  the  ore  is  not  very  acid  a  solu- 
tion of  caustic  soda  is  run  on  after  the  last  water-wash,  and  the  air 
contained  in  the  solution  will  serve  to  convert  the  ferrous  hydrate 
formed,  which  would  otherwise  subsequently  form  potassic  ferrocyanide 
4cp 


50  THE    CYANIDE    PROCESS.         • 

with  the  potassic  cyanide,  into  innocuous  ferric  hydrate.  If  very  acid, 
however,  aeration,  by  changing  to  another  vat,  will  be  necessary. 

"  Lime  sprinkled  on  the  surface  of  the  charge  of  ore,  or  mixed  with  it,, 
is  often  preferred  to  caustic  soda,  and  has  the  advantage  of  clarifying 
solutions  from  organic  compounds,  which,  if  present,  cause  'frothing' 
in  the  zinc  boxes.  Lime  does  not  form  the  yellowish-white  precipitate 
in  the  zinc  boxes,  which  is  mainly  ferrocyanide  of  zinc,  and  liable  ta 
occur  when  caustic  soda  is  used,  and  which,  by  coating  the  zinc,  inter- 
feres with  the  proper  precipitation  of  the  gold." 

The  Advisability  of  Ore  Concentration. — "  The  question  as  to  whether 
it«is  advisable  to  concentrate,  or  to  allow  the  pyrites  to  remain  with 
the  tailings  for  subsequent  cyanide  treatment,  is  at  present  under 
discussion,  and,  like  all  other  matters  in  gold  extraction,  resolves  itself 
into  a  question  of  cost.  The  general  rule  is,  that  with  high-grade  pyrites 
concentration  does  pay,  but  with  low-grade  not."  The  Nigel  Company 
has  abolished  the  use  of  concentrating  machinery.  They  found  that  the 
extraction  of  gold  by  cyanide  treatment  is  equally  as  good  from  the  ore 
from  which  the  concentrates  have  not  been  taken,  as  it  was  when  using 
True  vanner  concentrators.  Their  tailings  are  consequently  of  a  high 
grade,  containing  pyritic  matter,  and  solutions  of  greater  strength  are 
used  than  is  the  practice  with  other  works  on  the  Rand.    (W.  A.  Radoe.) 

The  Cyanide  Solutions. — "The  strength  of  the  solution  before  treat- 
ment was  some  four  years  ago  i  and  1  per  cent,  but  now  0.25  and  0.3 
per  cent  may  be  taken  as  the  usual  amount  of  pure  cyanide  of  potassium 
contained  in  what  are  usually  called  strong  solutions  in  South  Africa. 
In  most  works  a  constant  quantity  of  this  strong  solution  is  run  on 
each  charge  of  ore,  having  been  made  up  from  the  '  weak'  or  dilute  solu- 
tion in  stock  by  addition  of  a  sufficient  quantity  of  the  solid  salt,  or  a 
concentrated  solution  prepared  from  it.  Should  the  cyanide  consump- 
tion of  the  ore  increase,  the  strength  of  the  dilute  solution,  or  that  which 
has  been  already  used,  decreases,  and  more  solid  cyanide  is  required, 
and  vice  versa.  Another  method  consists  in  always  adding  the  same 
amount  of  solid  cyanide  to  the  same  amount  of  weak  solution,  and  in 
case  the  latter  is  below  a  certain  point  (say  0.1  per  cent)  to  continually 
use  a  larger  quantity  of  strong  solution  for  running  on  the  ore  until  the 
'weak'  rises  to  'normal'  once  more.  If  the  strength  of  the  stock  solu- 
tion falls  too  low,  the  precipitation  of  gold  is  imperfect,  probably  because 
the  cyanide  of  zinc  formed  in  the  precipitation  boxes  is  not  dissolved 
and  coats  the  zinc.  If,  on  the  other  hand,  it  is  too  high,  the  consump- 
tion of  cyanide  and  zinc,  by  dissolution  of  the  latter  in  the  former,  is 
unnecessarily  great.  In  this  case,  too,  the  loss  of  cyanide  by  atmos- 
pheric decomposition  is  increased,  and,  while  the  same  absolute  amount 
of  solution  is  lost  by  leakage  and  in  the  form  of  moisture  adhering  to  por- 
tions of  the  residues,  yet,  the  solution  being  stronger,  more  potassic  cyanide 
is  lost.  The  quantity  of  strong  solution  employed  per  charge  of  ore 
varies  according  to  whether  a  preliminary  washing  with  a  dilute  solution 
has  been  employed  or  not.  In  the  former  case,  it  is  about  25  per  cent  of 
the  weight  of  the  ore,  and  in  the  latter  case  about  40  per  cent,  which  last 
quantity  is  usually  sufficient  to  just  cover  the  charge.  The  amount,  how- 
ever varies  in  different  works,  and,  within  reasonable  limits,  it  is  not  a 
matter  of  great  importance,  provided  sufficient  solid  cyanide  is  added 
daily  to  keep  the  stock  of  weak  solution  at  the  right  strength.  It  is 
desirable  that  the  strong  solution  be  of  uniform  strength  throughout  the 


EXEMPLIFICATION   OF   PROCESS — THE    PROCESS   IN   AFRICA.  51 

whole  charge  of  ore,  and  this  object  is  attained,  in  great  measure,  by 
using  a  preliminary  washing  with  a  dilute* solution;  the  cyanide  of  the 
latter  satisfies  most  of  the  components  of  the  ore,  which  consume 
cyanogen,  so  that  the  strong  solution,  which  follows,  is  free  to  act  on 
the  gold  alone.  This  preliminary  wash  has  also  the  advantage  of  satu- 
rating lumps  of  slimes  which  may  be  in  the  tailings  and  would  absorb 
the  strong  solution,  which  would  be  lost  when  the  residues  are  dis- 
charged. Generally  speaking,  a  larger  quantity  of  the  weaker  solution 
is  preferable  to  a  smaller  quantity  of  strong  solution,  but  exigencies  of 
time,  capacity  of  the  plant,  filtering  properties  of  the  material,  etc., 
cause  modifications  of  this  rule.  When  a  charge  has  had  more  than  its 
own  weight  of  washings  passed  through  it,  it  becomes  a  question  whether 
there  is  suflBcient  increase  in  yield  by  continuation  of  the  process  to 
cover  the  cost  of  pumping,  apart  from  the  fact  that  if  the  solution  be 
run  too  fast  through  the  zinc  boxes  not  only  is  the  gold  it  contains 
imperfectly  precipitated,  but  that  already  deposited  is  liable  to  be 
haechanically  carried  into  the  sump  by  the  force  of  the  current." 

The  strength  of  cyanide  solutions  used  in  the  Crown  Reef  Mine  works 
varies  from  0.05  per  cent  to  0.35  per  cent;  they  range  after  treatment 
from  nothing  to  0.33  per  cent.  The  total  quantity  of  solution  used,  inclu- 
sive of  water-washes,  is  about  80  per  cent  of  weight  of  charge;  extraction 
takes  from  forty  to  fifty  hours.  (G.  E.  Webber,  Jr.)  In  the  Nigel 
Company,  where,  as  already  stated,  concentration  has  been  abandoned, 
the  conditions  are  in  consequence  somewhat  different  from  those  usually 
prevailing  in  cyanide  works;  for  tailings  over  24  dwts.  (about  $18)  in 
value  a  solution  of  0.6  per  cent  is  used,  preceded  by  a  weak  wash  of 
solution  of  0.15  per  cent  and  followed  by  two  weak  washes;  the  liquors 
drain  off  at  a  strength  of  from  0.4  to  0.25  per  cent  of  cyanide,  the  first 
solutions  draining  off  at  a  lower  percentage  than  the  last.  The  amount 
of  cyanide  used  per  ton  is  about  3.8  or  3.5  lbs.  per  oz.  of  gold  re.covered 
(3.5  lbs.  of  76  per  cent  cyanide).     (W.  A.  Radoe.) 

Precipitation  by  Zinc. — The  precipitation  process  going  on  in  the  zinc 
boxes  has  been  fully  discussed  in  a  former  part  of  this  paper. 

"  After  passing  through  the  zinc  box  the  solution  should  not  contain 
more  than  50  cents  of  gold  per  ton,  and  in  the  majority  of  cases  there  will 
be  only  a  trace  of  gold  present.  If  appreciable  quantities  of  gold  remain 
unprecipitated,  a  certain  amount  is  daily  lost  in  the  dilute  cyanide 
solution  contained  in  the  residues  (see  above).  The  latter  should  be 
periodically  tested  for  gold  soluble  in  water,  and  gold  soluble  in  cyanide 
solution;  imperfect  precipitation  will  be  discovered  by  the  first,  and  too 
short  time  of  treatment  by  the  second  test." 

Time  of  Treatment. — "The  total  time  employed  in  the  treatment  of 
a  charge  of  tailings  varies  from  three  days  to  a  week,  and  is  dependent, 
from  a  chemical  point  of  view,  upon  the  greater  or  less  fineness  of  the 
gold;  the  general  rule  is  that  the  longer  the  time  the  better  until  the 
increased  cost  of  treatment  more  than  counterbalances  the  improved 
percentage  of  extraction." 

Cyanide. — The  cyanide  usually  employed  contains  from  70  to  80  per 
cent  of  pure  potassic  cyanide,  but  another  quality,  containing  upward  of 
95  per  cent,  imported  from  Germany,  is  also  used,  and  is  preferable  for 
the  reasons  explained  in  the  chapter  on  cyanide  (p.  30).  The  consump- 
tion of  cyanide  is  about  150  tons  per  month  in  the  Witwatersrand  mines. 
Germany  has  sent  out  nearly  1,000  tons  to  the  Transvaal  this  year. 


52  THE    CYANIDE    PROCESS. 

Value  of  Rand  Tailings  and  Percentage  of  Extraction. — "The  average 
value  of  Rand  tailings  per  ton,  before  treatment,  is  $5;  of  this  $8,  or  60 
per  cent,  is  actually  obtained  by  the  cyanide  process,  $1  50,  or  30  per 
cent,  is  left  in  the  residue,  and  50  cents,  or  10  per  cent,  is  unaccounted 
for.  Ores  from  DeKaap,  containing  a  large  amount  of  mispickel,  gave 
only  an  extraction  of  9  per  cent,  but  on  roasting  the  extraction  rose 
to  83  per  cent,  the  arsenic  being  presumably  driven  off.  Owing,  however, 
to  the  cost  of  fuel,  and  the  high  cyanide  consumption  resulting  from 
sulphates  formed  by  partial  oxidation,  roasting  is  never  employed  as 
preliminarj^  to  the  cyanide  process.  The  percentage  of  gold  extracted 
varies  in  different  localities,  but  is  usually  between  70  and  80  per  cent. 
It  depends  chiefly  upon  the  degree  of  fineness  of  the  ore,  and  the  degree 
to  which  the  gold  it  contains  has  been  liberated  from  the  matrix  and 
exposed  to  the  action  of  the  solution.  (In  comparing  an  ounce  of  like 
particles  of  gV  i^-  diameter  with  an  ounce  of  particles  of  similar  shape 
but  -^  in.  diameter,  the  surface  exposed  by  the  first  lot  is  three  fourths 
of  the  surface  exposed  by  the  second  lot — this  being  a  particular 
instance  of  the  general  law,  that  for  equal  weights  of  similar  particles 
the  surface  exposed  varies  inversely  as  the  diameter.)  There  is  little 
doubt  that  the  remaining  20  to  30  per  cent  in  the  residues  consist  of 
particles  of  gold  still  incased  in  the  matrix,  and  this  is  proved  by  the 
fact  that  finer  grinding  renders  almost  complete  extraction  possible. 
The  limits  of  fine  grinding  on  a  working  scale  are  fixed  by  the  increased 
difficulty  of  filtration.  Even  when  only  a  No.  30  screen  is  used  in  a  wet- 
crushing  stamp-mill,  it  is  not  possible  to  filter  the  pulp  in  its  entirety, 
on  account  of  the  slimes;  the  consequence  of  this  is  that  with  mod- 
erately fine  crushing  only  the  coarser  portion  (possibly  80  per  cent) 
of  the  tailings  is  at  present  treated  by  cyanide.  Slimes  of  sufficient 
value  are  in  some  cases  treated  by  drying,  crushing,  and  mixing  with  a 
sufficient  amount  of  coarse  tailings  to  allow  filtration.  A  mixture  of 
equal  parts  of  each  take  at  least  a  week  for  treatment.  The  drying  is 
performed  either  by  exposure  to  the  sun,  or,  especially  in  the  case  where 
much  organic  matter  is  present,  by  slightly  calcining  in  a  reverberatory 
furnace,  or  in  form  of  bricks  in  a  kiln.  In  the  last  two  cases,  however, 
the  cyanide  consumption  is  increased  by  the  oxy-salts  of  iron  formed, 
and  although  usuall}''  remarkably  good  results  may  be  reckoned  upon, 
yet  the  cost  involved  in  so  much  handling  is  so  high  as  to  be  prohibitive 
for  low-grade  slimes."  The  treatment  of  slimes  or  of  tailings-pulp  con- 
taining a  high  percentage  of  slimes,  is  still  one  of  the  unsolved  prob- 
lems of  the  cyanide  process;  at  present  most  of  the  slimes  are  washed 
away,  and  with  them  a  large  amount  of  gold  is  lost  in  Johannesburg. 

It  has  been  suggested  to  solve  the  difficulty  of  slime  treatment  by 
mixing  the  slimes  with  50  per  cent  of  their  weight  of  a  solution  contain- 
ing cyanide  of  potassium  and  the  double  cyanide  of  manganese  and 
potassium.  This  mixture  is  pumped  into  a  filter  press  under  high 
pressure;  after  filling  the  press,  water  is  forced  through,  washing  out 
the  gold  solution.  An  extraction  of  97.6  to  98.2  per  cent  is  claimed. 
(W.  Bettel's  process.     E.  &  M.  J.) 

Loss  of  Gold,  and  its  Causes. — "From  leakage,  and  the  loss  consequent 
upon  the  handling  of  gold  slimes  in  the  various  stages  of  conversion 
into  bars  of  bullion,  there  is  a  certain  amount  of  loss;  but  this,  in  prop- 
erly conducted  works,  should  be  small.  Even  when  experimental  errors 
of  assay  be  also  taken  into  account,  the  discrepancy  between  theoretical 


EXEMPLIFICATION    OF   PROCESS THE    PROCESS   IN    AFRICA.  Oo 

extraction,  estimated  on  assay  and  tonnage,  and  actual  extraction  of 
fine  gold  contained  in  the  bullion,  should  not  exceed  3  to  4  per  cent. 
As  a  matter  of  fact,  chiefly  from  unskillful  work,  the  bullion  actually 
recovered  amounts  in  the  Rand  gold  fields,  on  an  average,  to  only  60 
per  cent;  whereas  the  average  extraction,  as  estimated  by  assaying  the 
material  before  and  after  treatment,  amounts  to  70  per  cent.  The  chief 
causes  of  error  in  the  estimate  of  extraction  arise  from  incorrectly  calcu- 
lating the  tonnage,  from  faulty  sampling  of  charges  and  residues,  and 
from  careless  assaying  of  too  small  samples.  If  truckloads  of  tailings 
be  weighed  periodically  and  the  percentage  of  moisture  carefully  tested; 
if  samples  of  tailings  before  treatment  be  taken  from  each  incoming 
truck  and  mixed  thoroughly,  and  the  residues  after  treatment  be  treated 
likewise;  and  if  assays  be  daily  made  in  duplicate  on  not  less  than  an 
assay-ton  of  material,  when  this  is  low  grade — then  there  should  be  little 
difference  between  estimated  and  actual  extraction,  provided  there  is  not 
much  leakage  and  the  gold  slimes  are  carefully  handled.  In  many 
works  a  serious  loss  is  incurred  by  allowing  solution,  containing  very 
fine  gold  slimes  in  suspension,  to  enter  the  general  stock  of  solution, 
and  to  be  ultimately  discharged  with  the  residues.  So  fine  is  some  of 
this  material  that  it  will  even  pass  through  the  finest  filter  cloth  and 
remain  suspended  after  hours  of  '  settling.'  The  most  effectual  way  of 
overcoming  this  difficulty  is  to  run  all  solution,  filtered  or  decanted, 
from  gold  slimes  during  the  process  of  'cleaning-up'  or  separating 
them  from  the  zinc,  into  a  separate  vat,  called  a  '  settler.'  This  is  left 
undisturbed  for  some  days,  after  which  the  supernatant  liquid  may 
be  safely  run  off'.  This  settler  should  equal  in  capacity  the  united  zinc 
precipitation  boxes,  and  may  be  cleaned  up  half-yearly.  Filter  presses 
are  sometimes  used  to  remove  as  much  solution  as  possible  from  the 
gold  slimes  before  drying  the  same."  In  large  works,  like  those  of  the 
Crown  Reef  Company,  the  actual  returns  of  bullion  amount  to  95  per 
cent  of  the  calculated  extraction.  It  is  explained  that  the  difference  in 
the  estimation  of  the  weight  of  tailings  treated  is  sufficient  to  account 
for  the  difference  of  5  per  cent  (G.  E.  Webber,  Jr.).  The  Nigel  Company 
recover  about  93  per  cent  of  the  calculated  extraction;  the  incomplete 
recovery  is  attributed  partly  to  the  "  soakage  "  of  the  vats,  and  particu- 
larly to  the  treatment  of  the  bullion,  the  slag  sometimes  containing  as 
much  as  two  hundred  ounces  to  the  ton,  of  which  only  from  60  to  70  per 
cent  are  recovered  by  amalgamation  in  a  grinding-pan  (W.  A.  Radoe). 

The  Zinc  for  Bullion  Precipitation  "  is  used  in  the  form  of  thread-like 
turnings,  obtained  as  before  described.  A  cubic  foot  of  them  weighs 
from  3  to  6  lbs.,  and  exposes  forty  square  feet  of  surface  per  pound 
weight.  Granulated  zinc  is  never  used,  as  it  exposes  a  very  small  sur- 
face in  proportion  to  its  weight  and  is  liable  to  clog  in  the  extractors. 
Aluminium  in  conjunction  with  an  electric  current  has  been  suggested, 
as  also  alternate  sheets  of  iron  and  lead  foil  between  which  a  current 
of  two  hundred  amperes  and  seven  volts  passes;  but  these  methods  are 
still  in  the  experimental  stage.  The  consumption  of  zinc  varies  greatly 
in  different  works,  and  is  dependent  upon  causes  other  than  the  amount 
of  gold  precipitated.  The  absolute  amount  varies  from  2  to  8  oz.  per 
ton  of  ore,  but  of  this,  owing  to  waste  in  cutting  out  and  turning,  prob- 
ably not  more  than  one  half  goes  actually  into  solution,  when  the  finely 
divided  zinc  included  in  the  gold  slimes  be  also  taken  into  account. 
The  precipitation  of  the  bullion  is  conducted  as  described  before.     The 


54  THE    CYANIDE    PROCESS. 

zinc  consumption,  above  the  amount  required  for  gold  precipitation 
by  the  equation  of  the  cliemical  reaction,  is  due  to  its  solution  in  the 
caustic  alkali  formed  as  indicated,  in  the  free  cyanide  and  caustic  alkali 
present  in  the  solution  as  it  issues  from  the  leaching  vats,  and  also  in 
its  precipitating  action  upon  other  substances  in  solution.  An  average 
ore  would  probably  consume  about  ten  times  as  much  zinc  as  it  yielded 
bullion,  but  if  in  treatment  caustic  soda  has  been  used  in  excess,  the 
consumption  will  necessarily  be  higher." 

Treatment  of  Precipitates — "Acid  is  occasionally  used  for  making  a 
complete  clean-up  of  all  the  zinc  contained  in  the  boxes,  and  also  for 
refining  the  amalgam  (zinc,  gold,  and  mercury)  formed  therein,  when 
the  tailings  have  contained  much  *  floured '  quicksilver.  Its  use,  for  refin- 
ing generally,  is  not  advocated  in  Johannesburg,  as  it  involves  washing 
and  filtration  of  the  slimes,  and  loss  of  gold  by  the  formation  of  regulus 
in  melting,  if  sulphates  have  remained  in  the  slimes  by  fault  of  imperfect 
washing.  The  method  most  in  use  for  refining  gold  slimes  in  the 
South  African  gold  fields  is  by  the  use  of  nitre.  The  slimes  are  dried 
till  just  before  they  become  dusty;  they  are  then  mixed  with  powdered 
nitre,  the  amount  varying  from  3  to  33  per  cent  of  their  weight,  and 
gently  heated  as  a  thin  layer,  either  in  a  wrought-iron  pipe  (10  in. 
diameter  by  6  ft.  length),  or  preferably  in  a  tray  of  wrought-iron  (f  in. 
thick,  by  6  ft.  by  3  ft.  by  1  ft.),  which  may  also  be  used  for  the  drying 
process.  In  neither  case  do  the  flames  come  into  direct  contact  with  the 
slimes;  a  hood  carries  off  the  obnoxious  fumes.  By  the  use  of  nitre 
everything  in  the  zinc  precipitation  boxes  which  passes  a  sieve  of  three 
of  four  meshes  to  the  lineal  inch  may  be  refined,  and  thus  the  finely 
divided  zinc,  which  otherwise  accumulates  and  clogs  in  the  boxes,  is 
constantly  removed.  Less  nitre  is  always  used  than  is  required  to 
oxidize  all  the  base  metals  present,  as  otherwise  the  free  nitre  will 
rapidly  corrode  the  plumbago  crucibles,  Avhich  subsequently  are  used 
for  melting;  it  is  advisable,  however,  to  remain  as  near  as  possible  below 
the  limit,  as  the  roasting  which  follows  is  thereby  conducted  quicker 
and  at  a  lower  heat.  Besides  rendering  the  bullion  finer — containing 
say  only  15  per  cent  base  metals — this  nitre-roasting  gives  a  cleaner 
slag  and  lessens  by  at  least  one  half  the  time  required  for  fusing  the 
gold  slimes,  and  prevents  violent  ebullitions  of  vapor  from  the  crucible. 
From  3,000  to  4,000  oz.  of  bullion  can  be  obtained  in  twenty-four  Jiours 
from  roasted  slimes  containing  33  per  cent  of  gold  by  the  use  of  No.  70 
plumbago  crucibles,  with  good  coke,  in  four  box  furnaces  (20  in.  square 
by  22  in.  deep).  The  following  fluxes  have  been  found  to  answer  well: 
When  much  metallic  oxide  is  present — slimes  six  parts,  borax  four 
parts,  soda  two  parts,  sand  one  part.  When  little  metallic  oxide  is 
present — slimes  three  parts,  borax  one  part,  soda  two  parts,  sand  one 
part.  The  function  of  the  sand  is  to  form  a  fusible  slag  with  the  soda, 
and  also  to  protect  the  pots  against  metallic  oxides  and  the  potash 
formed  by  the  reduction  of  the  nitre.  The  slag  resulting  from  melting 
slimes  usually  contains  an  appreciable  quantity  of  gold.  This,  in  the 
absence  of  smelting  works,  is  generally  crushed  by  hand  in  a  mortar  or 
by  power  in  a  smallest  size  Gates  or  Fraser  &  Chalmer's  sample  grinder. 
It  is  then  panned,  and  the  tailings  resulting,  still  rich  as  a  rule,  are 
shipped  to  Swansea.  In  estimating  the  cost  of  a  flux,  it  should  be 
remembered  that  a  very  small  percentage  of  gold  in  the  slag  will  pay 


1^    IS    10      S      o  Ifl  Ito  9o^__^o 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS   IN    AFRICA.  55 

for  an  improved  flux,  and  that  flux  which  gives  the  cleanest,  most  fluid 
slag  is  preferable." 

I  have  given  here  the  mode  of  bullion  treatment  in  Johannesburg  as 
described  by  the  African  Gold  Recovery  Company;  in  addition  to  it,  I 
refer  to  my  own  way  of  procedure,  as  given  on  page  36,  which  may  offer 
some  points  of  advantage. 

Fineness  of  Bullion. — The  bullion  in  the  Robinson  Works  is  about 
650  fine;  it  is  very  hard  and  brittle,  and  the  bars  are  by  no  means  uni- 
form, so  that  it  is  difficult  to  obtain  an  accurate  assay;  in  addition  to 
zinc,  they  contain  silver,  lead,  and  sometimes  a  little  copper  (Butters 
and  Clennell).  The  bullion  of  the  Crown  Reef  Company  is  950  fine 
(830  gold,  120  silver)  (G.  E.  Webber,  Jr.).  The  bullion  of  the  Nigel 
Company  has  been  on  an  average  795  fine  during  the  last  seven  months 
(W.  A.  lladoe). 

The  Cost  of  Treatment  "  varies  according  to  the  size  of  plant  and  the 
facilities  for  working,  but  exclusive  of  royalty  may  be  taken  at  from 
-$1  50  per  ton  for  a  5,000-ton  plant,  to  87-i  cents  per  ton  for  plants  treating 
20,000  tons  monthly." 

The  Cost  of  Plants  "varies  according  to  the  locality  and  the  style  in 
which  they  are  erected.  To  erect  an  average  size  plant  costs  at  Johan- 
nesburg about  $6  25  per  ton  of  ore  it  is  intended  to  treat  monthly;  for 
very  large  plants  the  cost  would  perhaps  be  $5  per  ton."  All  plants 
have  the  following  main  features:  Leaching  or  percolation  vats,  zinc 
boxes  for  bullion  precipitation,  sumps  or  tanks  for  storing  solutions, 
pumps  for  assisting  filtration,  and  pumps  for  transporting  the  liquids. 
The  difference  between  the  various  plants  consists  in  the  size,  form,  and 
material  of  the  vats,  the  system  of  charging  and  discharging  the  tail- 
ings, and  the  general  arrangement  of  the  different  parts  of  the  machinery. 
The  construction  of  vats  and  the  handling  of  tailings  has  been  discussed 
above.  In  reference  to  the  latter,  I  attach  details  of  discharging  ap- 
pliances, taken  from  "  Notes  on  Gold  Extraction,"  by  W.  R.  Feldtmann. 

The  General  Arrangement  may  be  of  different  kinds.  "The  most 
convenient  method  is  to  have  solution  vats,  leaching  vats,  extractors, 
and  sumps  in  four  tiers,  so  that  each  series  may  be  completely  drained 
into  that  next  below  it.  B}''  this  means  sufficient  solution  can  be  stored 
in  the  solution  vats,  and  sufficient  room  left  in  the  sumps  to  enable 
work  to  proceed  for  from  twelve  hours  to  twenty-four  hours  without 
pumping.  Many  plants,  however,  have  the  solution  vats  and  sumps  on 
the  same  level  as  the  leaching  vats;  in  this  case  the  solution  issuing 
from  the  last  mentioned  vats  is  run  through  precipitation  boxes  into  a 
small  tank  and  is  continually  pumped  back  when  required."  I  attach 
plates,  which  illustrate  the  variations  in  the  general  design  of  plants 
with  regard  to  the  relative  position  of  the  different  parts,  which  with 
their  explanation  are  taken  from  "  Notes  on  Gold  Extraction  by  means 
of  Cyanide  of  Potassium,  as  carried  out  on  the  Witwatersrand  Gold 
Fields,"  by  W.  R.  Feldtmann. 

"In  No.  1  design,  the  leaching  vats  are  placed  highest.  The  solution 
gravitates  from  these  through  the  zinc  boxes  into  the  storage  vats,  there 
to  be  made  up  to  strength  ready  for  pumping  up  to  the  leaching  vats 
again.  In  the  sketch  the  discharging  of  the  tanks  is  assumed  to  be  done 
over  the  side.  In  No.  2  design  the  solution  is  either  pumped  direct 
from  the  leaching  vat,  or,  running  into  a  small  sump  or  an  air-tight 
receiver,  is  pumped  from  there  into  zinc  boxes,  and  runs  thence  into* 


56 


THE   CYANIDE    PROCESS. 


^a 


l/AR/AT/O/V/y^  9. 


— /)FSfc  Afs  or  crA  /v/d£'pl  a  a/ts.  - 


i?es/  cAfS  or  cyAr///?j>'/>AAA/TS. . 


V  V  y    '  ^ 


_ao 


^0 


overhead  storage  vats.  Having  been  made  up  to  strength,  it  is  ready 
to  run  direct  into  the  leaching  vats  again.  The  discharge  system  indi- 
cated is  the  '  bottom  discharge.'  No.  3  design  is  a  combination  of  the 
two  previous  ones,  and  is  advantageously  fitted  with  a  pipe  service  to 
enable  one,  if  desired,  to  run  solutions  up  through  the  sand  in  the 
leaching  vats.  As  shown  in  the  sketch,  the  plant  is  designed  for  side 
discharge;  but  of  course  any  system  of  discharge  may  be  applied  to 
any  of  the  three  arrangements  of  plant. 


EXEMPLIFICATION    OF   PROCESS — THE   PROCESS   IN   AFRICA. 


57 


gji  15   TO   y    y         ^p        %°       So 4o 


58 


THE    CYANIDE    PROCESS. 


Buildings. — "  The  majority  of  plants  now  erected  have  only  the  zinc 
boxes  inclosed  in  buildings,  and  there  is  little  objection  to  having  no 
weather  protection  when  cemented  vats  only  are  used,  but  with  wooden 
vats,  exposure  to  the  sun  and  weather  undoubtedly  causes  increased 
leakage. 


-pv:7i.  rELDT/iAAryv-'- 


S/Z)r2?/SC//yi/)GE  4-r/^jE:/9CO^./l'r/OA^J<^7'S 


■SCyt/  f  7  //vcAy^^Trcor- 


Lahor. — "The  men  employed  in  a  plant  of  average  capacity  (5,000 
tons  per  month)  are:  One  manager,  one  assayer,  two  shift  men,  one 
mechanic,  two  native  gangers,  and  the  native  crew."  The  Nigel  Com- 
pany employ  two  white  men  of  twelve-hour  shifts  in  the  works,  whose 
duty  it  is  to  "  make-up,"  pump  in,  and  drain  ofl"  solutions,  and  to  attend 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS    IN    AFRICA. 


59 


Cn.IiUTTEES' BOTTOM  DISCHARGE  AT PERCOLATTOy  VATS. 


n./j.iRrjyES  bottom  discuau<ie  at fercolation  vats . 

Cop.  fkom  W R  FELTMANN'C-    Nohi.  On  Gold  Extraction"  Ltc. 


60  THE   CYANIDE    PROCESS. 

to  things  generally,  and  one  white  overseer  over  the  natives  (about 
thirty  in  number),  who  attends  to  charging  and  discharging  the  vats 
(W.  A.  Radoe).  The  Crown  Reef  Company  employ  one  white  man  per 
shift  of  eight  hours  and  seventy  native  laborers,  handling  500  tons  of 
tailings  (G.  E.  Webber,  Jr.).  During  1893  about  500  vats  were  in  use 
on  the  South  African  gold  fields,  of  a  total  daily  capacity  of  11,000  tons. 

Results  of  the  Process. — The  process  of  treating  tailings  by  cyanide  was 
first  introduced  on  the  Transvaal  gold  fields  in  1890;  the  output  of  gold 
by  its  means  has  since  taken  on  enormous  proportions.  The  gold  pro- 
duced by  cyanide  in  1890  amounted  to  286  oz.;  in  1891  to  34,862  oz;  in 
1892  to  178,688  oz.;  in  1893  to  330,510  oz.;  and  during  the  first  six 
months  of  1894  to  317,950  oz.  I  inclose  a  table  giving  the  output  of 
gold  in  the  Witwatersrand  district  by  the  milling  and  cyanide  process. 
The  value  of  cyanide  gold  is  on  an  average  $15  per  oz.  The  total  value 
produced  by  cyanide  at  the  end  of  June  amounted  to  $12,934,440.  This 
enormous  amount  has  been  almost  entirely  derived  from  low-grade  tail- 
ings, which  were,  before  the  introduction  of  MacArthur-Forrest'smethods, 
practically  valueless,  for  want  of  cheap  and  efficient  means  of  extraction. 
The  working  cost  of  treatment  by  the  process  is  the  lowest  known  in  the 
history  of  gold  metallurgy,  roasting  never,  and  preliminary  treatment 
in  exceptional  instances,  being  required.  The  process  is  adopted,  only 
amongst  others,  by  the  following  mines: 

Robinson  Company,  60  stamps;  in  1892,  101,061  tons  were  crushed, 
yielding  98,799  oz.  of  gold,  an  average  of  19  dwts.  13^  grs.  per  ton; 
the  concentrates  yielded  8,407  oz.,  and  75,375  tons  of  tailings  by  cyanide 
treatment  27,577  oz.;  the  average  from  all  sources  was  1  oz.  6  dwts.  16 
grs.  per  ton;  the  cost  per  ton  about  $5  50. 

The  Langlaagte  Estate  Company,  with  120  stamps  working,  crushed 
in  1892,  197,201  tons,  yielding  on  an  average  6  dwts.  23.81  grs.  per 
ton;  twelve  thousand  tons  of  tailings  are  being  worked  per  month  at  a 
working  cost  of  $1  per  ton;  this  plant  is  being  increased  to  treat 
thirty  thousand  tons  monthly;  the  total  value  of  gold  received,  includ- 
ing that  from  treatment  of  tailings  by  cyanide,  amounted  in  1892  to 
$1,554,850.  The  Langlaagte  Estate  Company  has  been  using  cement 
tanks  with  good  results  for  sometime  past;  the  vats  and  sumps  are  built 
in  excavations  made  in  solid  ground,  the  upper  part  being  level  with 
the  ground.  A  tram-line  runs  over  the  center  of  five  large  vats,  each 
holding  450  tons,  for  charging  purposes.  A  steam  crane,  running  on 
rails,  placed  on  each  side  of  these  vats,  lifts  and  empties  the  tailings, 
after  treatment,  into  a  movable  chute  placed  over  two  parallel  lines  of 
trucks.  This  chute  fills  two  trucks  at  each  lift  at  a  cost  of  less  than  2 
cents  per  ton,  including  wear  and  tear  and  maintenance  of  the  machinery . 
The  time  necessary  to  empty  each  vat  is  fourteen  hours. 

The  following  description  of  the  application  of  the  cyanide  process  in 
the  very  extensive  works  of  the  Langlaagte  Estate  and  Gold  Mining 
Company  in  Johannesburg  is  derived  from  notes  written  by  the  com- 
pany's assayer,  Mr.  Thomas  Lockhart,  which  have  been  contributed  by 
the  company's  manager,  Mr.  James  Ferguson,  whilst  this  paper  was  in 
press: 

The  ore  is  of  a  silicious  nature,  containing  about  2  per  cent  of  iron 
pyrites,  and  very  little  base  matter;  it  is  not  treated  directly  by  cyanide, 
but  is  first  put  through  the  battery-amalgamation  process.  Eight  hun- 
dred tons  are  crushed  daily.     The  tailings  leaving  the  plates  are  con- 


EXEBIPLIFICATION    OF    PROCESS — THE    PROCESS    IN    AFRICA.  61 

centrated,  and  then  run  to  three  settling  dams,  each  of  which  holds 
7,000  tons.  The  slimes  are  here  separated  from  the  tailings  and  allowed 
to  run  away,  as  they  are  greatly  impeding  the  percolation  of  the  cyanide 
solution  in  the  vats.  The  tailings,  free  from  slimes,  are  hauled  from 
these  dams  in  trucks,  by  means  of  two  endless  steel  wire  ropes,  and  run 
onto  an  overhead  tram-line,  from  where  they  are  dumped  directly 
into  the  vats  for  treatment.  The  vats  are  built  in  excavations;  their 
tops  are  level  with  the  surface  of  the  gi'ound.  Of  these  vats  there  are 
fifteen;  they  are  built  of  brick,  and  circular  in  form,  of  a  diameter  of  40 
ft.,  and  a  depth  of  9  ft.  3  in.  Their  sides  are  cemented,  and  the  bottoms 
laid  with  concrete;  the  latter  slope  gently  to  one  side,  where  a  2  in.  pipe 
carries  off'  the  solutions.  The  bottoms  are  covered  with  a  filter-bed, 
built  of  stones,  about  3  in.  deep,  which  are  packed  close  together  and 
form  a  level  surface,  which  is  covered  with  cocoa  matting.  Each  vat 
holds  about  450  tons  of  tailings,  which  remain  in  them  under  treatment 
for  three  days.  After  the  completion  of  the  extraction,  the  residues  are 
discharged  by  means  of  trucks,  which  are  lowered  into  the  vats,  filled 
by  Kaffirs,  hoisted  up  by  a  crane,  and  run  out  on  the  dump  by  means 
of  an  endless  rope. 

As  a  rule  three  vats  are  charged  per  day  and  three  discharged. 
During  March  33,000  tons  of  tailings  were  treated  on  31  working  days, 
or  1,064  tons  per  twenty-four  hours.  These  tailings  averaged  before 
treatment  4  dwts.  5  grs.  of  gold  per  ton;  the  residues,  after  treatment, 
contained  17  grs.,  which  corresponds  with  an  extraction  of  83  per  cent, 
but  only  68  per  cent  of  the  assay  gold-value  was  actually  recovered. 
The  chief  causes  of  the  incomplete  recovery  of  the  gold  are:  The  imper- 
fect precipitation  by  zinc;  the  presence  of  slimes  in  the  tailings,  which 
take  up  and  retain  some  of  the  cyanide  gold  solution;  the  loss  of  gold 
solution  through  leakages  in  tanks  and  pipes;  and  the  mechanical 
losses  in  manipulating  the  precipitates  in  drying,  calcining,  and  melting. 

The  strength  of  the  first  or  strong  cyanide  solution  pumped  onto 
the  tailings,  varies  from  0.32  to  0.38  per  cent;  it  stands  3  or  4  in.  above 
the  surface  of  the  charge,  and  remains  in  contact  for  from  eight  to  twelve 
hours;  after  that  time  it  is  run  off  and  passes  through  the  zinc  precipi- 
tation boxes;  it  is  then  brought  up  to  its  original  strength  by  adding 
cyanide  of  potassium  and  used  again  on  a  next  charge.  The  zinc  boxes 
are  18  ft.  long  by  5  ft.  wide  and  2^  ft.  deep,  and  contain  the  usual  divis- 
ions.    Five  such  boxes  take  the  solution  from  ten  vats. 

The  first  part  of  the  solution,  when  running  off  the  charge,  contains 
about  0.02  per  cent  cyanide;  the  following  portions  are  of  greater  strength 
and  rise  up  to  0.3  per  cent.  When  the  solution  has  drained  off,  the 
second,  or  weak,  solution,  of  about  0.2  per  cent  cyanide,  is  pumped  on; 
this  percolates  directly  through  and  replaces  the  first  solution,  which  has 
remained  in  the  material.  A  water-wash  completes  the  treatment.  This 
wash  remains  in  contact  during  some  hours,  and  is  then  drained  off  as 
usual;  it  forms  the  weak  or  second  solution  for  a  following  charge. 

The  solutions  are  stored  in  vats  56  ft.  in  diameter  and  9  ft.  3  in.  in 
depth.  The  consumption  of  cyanide  amounted  during  the  last  six 
months  of  1893  to  0.55  lb.  per  ton  of  tailings. 

The  treatment  of  the  concentrates  (sulphurets)  is  conducted  on  the 
same  plan  as  that  of  the  tailings.  Two  tanks,  each  35  ft.  in  diameter 
and  2\  ft,  deep,  serve  the  purpose.  A  solution  of  0.6  per  cent  cyanide 
is  used;  this  remains  in  contact  with  the  material  for  six  hours;  it  is 


62  THE    CYANIDE    PEOCESS. 

then  run  oflf  and  the  gold  precipitated  as  usual  in  the  zinc  boxes,  which 
are  11  ft.  long,  2  ft.  deep,  and  2  ft.  wide.  The  solution  is  then  restored 
to  the  required  strength  and  used  over  and  over  again  till  the  assays  of 
the  residues  prove  the  termination  of  the  extraction. 

During  the  month  of  March  405  tons  of  concentrates  were  treated; 
they  averaged  before  treatment  2  ozs.  10  dwts.  4  grs.  of  gold  per  ton; 
the  residues  contained  5  dwts.  14  grs.,  which  corresponds  with  an  ex- 
traction of  89  per  cent  of  the  assay- value;  this  percentage  is  actually 
recovered.  The  consumption  of  cyanide  per  ton  of  concentrates 
amounted  during  the  last  half  of  the  year  1893  to  0.5  lb.  The  cyanide 
used  contains  98  per  cent  of  potassium  cyanide.  The  zinc  used  for  pre- 
cipitating the  gold  contains  1-^  per  cent  impurities;  it  is  applied  in 
filiform.  For  every  one  ounce  of  fine  gold  obtained  1.48  lbs.  of  zinc  are 
consumed.  Cleaning  up  takes  place  twice  a  month.  The  gold  precipi- 
tates, mixed  with  finely  divided  zinc,  are  separated  from  the  coarse  zinc 
by  shaking;  they  are  then  dried  and  calcined.  The  calcination  is  carried 
on  on  a  heavy  iron  plate,  which  is  heated  to  redness;  it  is  continued  till 
the  oxidation  of  the  zinc  is  complete.  The  calcined  mass  is  then 
fused  with  borax,  soda-ash,  and  sand.  The  mixture  is  charged  into  No. 
50  plumbago  crucibles  and  melted  in  a  reverberatory  hearth  furnace, 
which  holds  twenty-two  crucibles  at  a  time.  The  time  required  for  melt- 
ing varies  from  one  and  a  half  to  three  hours,  according  to  the  character 
of  the  material  and  the  temperature  of  the  furnace.  The  molten  mass 
is  poured  into  iron  moulds;  the  bullion,  thus  obtained,  is  remelted  into 
bars  of  600  oz.  The  fineness  of  the  bullion  varies  considerably;  that 
obtained  from  tailings  runs  from  700  to  780;  that  from  concentrates 
from  750  to  820  fine.  The  weight  of  the  fluxed  precipitates  which  are 
reduced  per  month  amounts  to  about  9,000  lbs.  Three  shifts,  of  two 
white  men  each,  attend  to  the  working  of  the  process.  Two  twelve- 
hour  shifts,  of  five  Kafiirs  each,  are  constantly  employed  in  cutting 
zinc  shavings.  The  charging  and  discharging  of  the  percolation  vats  is 
done  by  contract;  14  white  men  and  250  Kaffirs  are  employed  for  the 
purpose.  The  buildings  consist  of  wooden  frame  structures,  covered  on 
all  sides  with  corrugated  iron. 

The  Langlaagte  Company  pays  a  royalty  for  the  use  of  the  Mac- 
Arthur-Forrest  patents,  amounting  to  $1  25  per  standard  ounce  of  gold 
extracted  from  tailings,  and  62|  cents  per  standard  ounce  of  gold 
extracted  from  sulphurets. 

The  Ferreira  Company  derived  for  the  half  year  ending  March  31, 

1892,  a  profit  of  $22,030  on  the  treatment  of  15,310  tons  of  tailings, 
producing  3,495  oz.  of  gold  at  a  cost  of  $2  91  per  ton.  Fort  he  year 
ending  March  31,  1893,  the  tailings  treated  by  cyanide  yielded  11,201  oz. 
of  gold,  which  means  to  say  4,592  dwts.  of  the  value  of  -$4  16  per  ton. 

The  Crown  Reef  Company  has  210  stamps  working.  For  the  half 
year  ending  March  31,  1893,  the  tailings  treated  by  the  process  yielded 
16,629  oz.  of  gold.  The  revenue  from  tailings  and  concentrates 
amounted  to  92  cents  per  ton. 

The  Henry  Nourse  Company  treated,  during  the  first  six  months  of 

1893,  12,640  tons  of  tailings  by  cyanide,  yielding  3,040  oz.,  or  4.81  dwts. 
of  gold,  at  an  average  cost  of  $2  33  per  ton. 

The  Meyer  and  Charlton  Company  treated  during  six  months  ending 
June  30,  1893,  10,799  tons  of  tailings  by  the  cyanide  process,  yielding 
3,205  oz.,  or  5.93  dwts.  per  ton. 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS    IN   AFRICA.  63 

The  Nigel  Company  obtained  during  twelve  months  21,471  oz.  of  gold 
by  the  process  from  tailings  and  concentrates. 

The  Rand  Central  Ore  Reduction  Company  has  been  formed  to  pur- 
chase tailings  from  companies  who  have  not  erected  their  own  plants; 
1,500  tons  of  tailings  are  treated  in  their  works  per  twenty-four  hours. 
The  vats,  made  of  wood,  hold  from  75  to  600  tons.  The  tailings  average 
5  dwts.  before  and  1  dwt.  after  treatment.  The  strong  solutions  contain 
about  0.3  per  cent,  the  weak  about  0.15  per  cent  of  cyanide.  The  last  solu- 
tion runs  off  at  about  0.08  per  cent.  All  solutions  together  amount  to 
about  1  ton  per  ton  of  ore.  The  extraction  takes  about  three  days.  The 
cyanide  used  is  of  98  per  cent  on  the  average.  The  extraction  from  the 
tailings  varies  from  75  to  80  per  cent  of  the  assay-value,  of  which  80  per 
cent  are  actually  recovered;  the  clean-up  is  never  complete  and  much 
gold  remains  in  the  slag.  The  zinc  consumption  amounts  to  about  1  lb. 
per  ounce  of  gold  recovered.  Electricity  is  also  used  for  bullion  precipi- 
tation. The  bullion  after  melting  is  750  to  850  fine.  The  total  cost  of 
treatment  is  about  $1  per  ton.  The  cost  of  the  plant  amounted  to  $600,- 
000;  200  white  men  and  800  Kaffirs  are  employed.     (D.  Ruston.) 

The  Langlaagte  Royal  Gold  Mining  Company  is  erecting  a  cyanide 
plant  for  the  treatment  of  10,000  tons  per  month.  The  mentioned  com- 
panies, in  conjunction  with  a  number  of  others,  more  or  less  important, 
treat  upwards  of  200,000  tons  of  tailings  monthly.  During  June,  1894^ 
220,507  tons  w^ere  treated,  with  an  average  yield  of  $3  per  ton.  The 
treatment  of  concentrates  by  chlorination  has  been  abandoned  in  favor 
of  cyanide  treatment  by  the  Crown  Reef  and  the  Langlaagte  Estate 
works. 

The  large  profits  accruing  to  some  of  the  mining  companies  are  to  a 
large  extent  derived  from  their  tailings-treatment.  Individual  returns 
show  that  at  several  of  the  leading  and  most  prosperous  mines  35  to 
50  per  cent  of  their  output  is  due  to  their  using  the  cyanide  process. 
The  Nigel  Company's  official  report  for  the  three  naonths  ending 
September  30,  1893,  shows  that  a  net  profit  of  $122,325  was  made,  of 
which  only  $43,970  was  derived  from  amalgamating,  and  $73,895  from 
cyanide  treatment  of  tailings  and  concentrates.  The  report  of  the  Lang- 
laagte Estate  Company  for  the  same  period  shows  a  net  profit  of  $51,410, 
derived  from  the  same  source.  During  1892,  37,595  oz.  were  recovered 
by  the  process  from  Robinson  tailings,  19,482  oz.  from  Crown  Reef,  and 
nearly  29,000  oz.  from  Nigel  tailings.  All  companies  mentioned  use  the 
cyanide  process  as  described  in  the  MacArthur-Forrest  patents,  and  use 
zinc  as  bullion  precipitant.  The  amount  of  gold  recovered  by  the  Mol- 
loy  process  (see  page  38)  is  insignificant.  The  two  companies  which 
were  described  in  the  official  list  of  the  Witwatersrand  Chamber  of 
Mines  as  using  that  process,  are  now  mentioned  as  using  the  MacArthur- 
Forrest  process. 

The  cyanide  plants  at  Johannesburg  are,  generally  speaking,  very 
similar  to  each  other  in  their  construction,  and  the  description  of  a 
typical  one,  that  of  the  Robinson  Company,  will  sufficiently  illustrate 
their  construction.  The  plant  in  question,  of  which  the  attached  plans 
were  designed  by  Mr.  Chas.  Butters,  consists  of  twelve  circular  open 
leaching  vats,  each  having  a  capacity  of  2,000  cub.  ft.  and  holding 
100  tons  of  tailings  and  cyanide  solution.  The  vats,  built  upon  elevated 
arched  stone  foundations,  are  filled  from  a  high  level  tramway  above 
them,  and  emptied  through  trapdoors  in  the  center  into  tramcars  below. 


64  THE    CYANIDE    PROCESS. 

Next  in  order  is  a  series  of  precipitating  boxes,  designed  to  continu- 
ously precipitate  gold  from  the  solution  as  it  passes  from  the  leaching 
vat  to  the  sump.  The  boxes  are  20  ft.  long,  2  ft.  wide,  and  2  ft.  deep; 
they  have  inclined  bottoms.  They  are  divided  into  compartments  a 
20  in.  in  length  each.  Each  chamber  contains  about  40  lbs.  of  zinc  turn- 
ings. Seven  compartments  in  each  box  are  filled  with  shavings;  of 
single  compartment  at  the  head  is  left  empty  to  receive  any  sand  that 
may  be  carried  through  the  filter  by  the  solution  from  the  tanks.  A 
double  compartment  at  the  foot  is  also  left  empty  to  allow  any  gold  that 
may  be  carried  away  by  the  stream  of  liquid  to  deposit  before  the  solu- 
tion flows  into  the  sump.  About  60  tons  of  solution,  which  is  the  quan- 
tity required  for  treating  the  ordinary  daily  charge  of  225  tons  of 
tailings,  is  allowed  to  run  through  two  zinc  boxes  in  about  nine  hours. 
This  solution  may  carry  from  1  oz.  to  3  oz.  of  gold  per  ton  of  liquid; 
after  passing  through  the  zinc  boxes  it  rarely  contains  more  than  $2, 
and  should  not  contain  more  than  50  cents  if  the  precipitation  has  been 
properly  carried  out  (Butters  and  Clennell).  Underneath  the  leaching 
vats  are  four  200-ton  sumps,  brick  and  cemented  tanks  set  in  the  ground. 
In  these  sumps  are  prepared  and  stored  the  solutions  for  dissolving  and 
washing  out  the  gold.  On  the  top  of  them  are  placed  a  double  set  of 
duplex  pumps,  so  arranged  that  both,  or  either,  will  throw  from  any 
sump  into  any  leaching  vat.  On  the  tram-level  above  the  vat  is  a  10 
horse-power  double-drum  winding  engine  and  boiler,  employed  to  hoist 
the  tailings  out  of  the  settling  pits.  The  plant  includes  four  furnaces 
of  large  capacity  for  smelting  and  refining  bullion;  also  a  laboratory 
a,nd  weighing-room.  An  elaborate  system  of  tram-lines  is  laid  down,  on 
both  high  and  low  levels,  for  delivering  and  discharging  the  tailings  in 
the  most  direct  and  efficient  manner.  Works,  pits,  and  dumps  are 
lighted  by  electric  light.  Lathes  for  turning  zinc  are  employed,  and  a 
12  horse-power  engine,  with  16  horse-power  boiler,  supply  all  power. 
The  whole  is  covered  by  an  airy  building  of  wood  and  iron.  The 
methods  of  working  are:  Hoisting  tailings  and  filling  vats;  pumping 
cyanide  solution  onto  the  tailings  in  the  vats  to  dissolve  the  gold;  run- 
ning ofl'  this  gold  solution  into  zinc  boxes  and  precipitating  the  gold; 
return  of  the  cyanide  solution  into  the  sump  below  for  repeated  use; 
collecting,  melting,  and  refining  the  precipitated  gold  (M.  S.  P.). 

The  report  of  this  company  for  the  year  ending  December  31,  1893, 
shows  that  55,200  tons  of  tailings  were  treated  by  the  cyanide  process, 
yielding  17,921  oz.  of  gold.  The  cost  at  the  cyanide  works  is  given  per 
ton  of  tailings  treated,  as  follows:  Wages,  29.62  cts.;  supplies,  12.24  cts.; 
fuel,.  10.48  cts.;  cyanide,  48.38  cts.;  zinc,  2.26  cts.;  filling  and  discharg- 
ing vats,  37.62  cts.;  royalty,  16.38  cts.;  total  cost,  173.86  cts.  per  ton. 
The  actual  cost  of  treatment  per  ton,  omitting  royalty,  was  156.98  cts. 
The  average  extraction  by  the  process  M'as  68.7  per  cent  of  the  assay- 
value  of  the  tailings.  An  innovation  in  percolation  in  the  Robinson 
Works  consists  in  the  circulating  system,  which  has  been  described  by 
Butters  and  Clennell  as  follows: 

"  It  has  been  stated  that  in  the  usual  method  of  working  about  a  ton 
of  solution  is  employed  in  the  treatment  of  a  ton  of  ore.  Since,  with 
free-milling  ore,  a  much  smaller  quantity  is  sufficient  to  dissolve  the 
same  percentage  of  gold,  it  was  suggested  that  the  solution  from  one 
tank  might  be  transferred  to  a  second,  and  be  made  to  dissolve  an  addi- 
tional quantity  of  gold  before  being  passed  through  the  zinc  boxes;  for 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS   IN    AFRICA. 


65 


example,  it  was  found  at  the  Robinson  Works  that  20  tons  of  solution 
were  amply  sufficient  to  extract  40  oz.  of  gold  from  75  tons  of  tailings  in 
one  tank.  It  was  found  that  20  tons  of  solution  sufficed  to  fill  a  tank 
holding  the  usual  charge  of  75  tons  of  tailings,  covering  the  charge  to  a 
depth  of  three  or  four  inches.  Instead  of  replacing  these  20  tons  of 
solution  by  fresh  cyanide,  the  solution  filtering  through  was  continually 
pumped  back  again  into  the  same  tank  for  about  thirty-six  hours  and 
then  passed  through  the  zinc  box.  The  extraction  of  gold  by  this 
circulation-system  was  equal  to  that  obtained  by  the  ordinary  method, 
and  the  consumption  of  cyanide  was  much  less,  since  a  much  smaller 
quantity  of  solution  was  exposed  to  the  action  of  the  zinc.  A  further 
modification  suggested  itself,  namely,  the  transference  of  the  solution 
charged  with  gold  from  one  tank  to  a  second  and  third,  in  order  that  it 
might  take  up  an  additional  quantity  of  gold  from  fresh  tailings  before 
passing  into  the  zinc  boxes.  The  advantages  of  this  method  are  that 
the  solutions  from  which  the  precipitate  is  obtained  are  much  richer  in 
gold,  giving  a  cleaner  deposit  on  the  zinc,  with  much  less  consumption 
of  cyanide." 

In  the  Durban-Roodeport  Company's  works  the  extraction  ranged 
from  67  to  85  per  cent.  The  cost  of  treating  the  tailings,  including 
patent-royalty,  amounted  to  $1  54;  the  profit  to  $2  87  per  ton.  During 
eleven  months,  in  1893,  79,765  tons  of  tailings  were  treated,  producing 
22,751  oz.  of  gold,  adding  about  33  per  cent  to  the  total  revenue. 

The  New  Chimes  Gold  Mining  Company  have  commenced  to  treat 
their  tailings  in  their  own  cyanide  works  only  since  the  beginning  of 
the  year;  during  March,  4,180  tons  of  tailings  realized  709.55  oz.  of 
bullion.  The  assay-value  amounted  to  (fine  gold)  3.33  dwts.;  fine  gold 
saved,  2.25  dwts.;  extracted,  67.56  per  cent;  lost  in  tailings,  32.44  per 
cent;  value  of  bullion  per  ton  treated,  $2  36;  expenses,  $1  02;  profit  per 
ton,  $1  32.     (G.  Halford  Smith.) 

The  financial  success  of  the  cyanide  process  in  South  Africa  is  best 
proved  by  the  dividends  paid  by  the  mining  companies  which  use  cya- 
nide for  tailings  treatment.  The  following  is  a  list  of  dividends  paid 
during  1893  by  companies  under  such  conditions: 


Names  of  Companies. 


Dividends. 


Amount- 
ing to — 


City  and  Suburban 

Crown  Reef... 

Durban-Roodeport 

Ferreira 

Langlaagte  Estate. 
Meyer  &  Charlton  . 

New  Primrose 

New  Rietfontein... 

Robinson 

Nigel -- 


100  per 
50  per 
4.5  per 

KX)  per 
30  per 
fiO  per 
40  per 
25  per 
8  per 
50  per 


cent 
cent 
cent 
cent 
cent 
cent 
cent 
cent 
cent 
cent 


1425,000 
300,000 
282,250 
225,000 
705,000 
215,100 
391,870 
200,000 

1,087,500 
400,000 


The  total  output  of  the  Rand  mines  fOr  the  year  ending  June  30, 1893, 
apart  from  the  cyanide  process,  was  1,087,058  oz.;  by  the  process  this 
quantity  was  increased  by  226,078  oz.,  making  a  total  of  1,313,136  oz. 
From  districts  not  included  in  the  Rand  proper,  a  further  recovery  of 
2,395  oz.  was  returned,  making  in  all  228,473  oz.  due  to  the  working  of 
the  process.  It  will  thus  be  seen  that,  by  the  use  of  the  process,  the 
Rand  production  was  increased  by  21  per  cent.  At  several  of  the  lead- 
5cp 


66  THE   CYANIDE   PROCESS. 

ing  and  most  prosperous  mines,  35  to  50  per  cent  of  their  gold  output  is 
due  to  the  use  of  cyanide.  The  report  of  the  Witwatersrand  Chamber 
of  Mines  gives  the  output  of  that  district  of  the  Transvaal,  for  March  of 
this  year,  at  165,372  oz.,  from  fifty-three  mines  and  three  custom  works; 
of  which  44,664  oz.,  of  the  value  of  $668,655,  were  extracted  by  cyanide 
from  204,421  tons  of  tailings,  and  1,367  oz.,  of  the  value  of  $20,805,  from 
concentrates  by  the  same  means.  The  returns  per  ton  of  tailings  aver- 
aged 4.37  dwts.;  33.74  per  cent  of  the  total  month's  production  of  gold 
is  derived  from  very  low-grade  material  by  the  process.  The  cyanide 
process  is  the  only  one  which  is  successfully  treating  tailings  on  a  com- 
mercial scale.  Its  economical  importance  for  Johannesburg  will  be 
evident  from  the  following  tables: 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS   IN    AFRICA. 


67 


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68 


THE    CYANIDE    PROCESS. 


Table  showing  Companies  in  the  Transvaal  Treating  Tailings  and  Concentrates  by  Cyanide 

in  1893. 


Company. 


Tons. 


Total  Output  in  ounces  for  1893. 


Plates. 


Concen- 
trates. 


Tailings. 


Champ  d'Or 

City  and  Suburban 

Crown  Reef 

Durban-Roodeport 

Evelyn 

Ferreira 

Geldenhuis  Main  Reef.. 

Gipsy - ■ 

Henry  Nourse 

J.  H.  Burg,  Pioneer 

Jubilee 

Langlaagte  Estate 

Langlaagte  Block  B 

Marais  Keef 

May  Consolidated 

Meyer  &  Charlton 

New  Heriot 

New  Chimes 

New  Primrose 

New  Rietfontein  Estate . 

New  Spec  Bona 

Nigel • 

Orion 

Paarl  Central— 

Randfontein -. 

Robinson 

Salisbury 

Simmer  &  Jack  - ■ 

Stanhope -.-  

Treasury ■ 

Village  Main  Reef 

Vulcan 

Wemmer 

Witwatersrand.-- 

Customs  Works 


17,896 

49,805 

118,244 

78,651 


5,722.7 
37,777.14 
51,688.0 
37,883.6 


723.2 


47,376 
9,495 
3,931 
19,749 
17,606 
43,673 

222,732 
64,066 
935 
60,298 
34,197 
21,455 
33,641 

141,464 
24,048 
2-2,289 
22,273 
34,657 


43,978.1 

3,417.7 

1,563.6 

15,329.18 

9,073.0 

24,774.10 

65,812.12 

19,621.4 

937.5 

24,957.4 

27,328.12 

14,089.2 

14,510.9 

57,574.8 

28,168.12 

8,784.5 

25,455.0 

8,318.3 


36.0 

9,047.11 

100.0 


79.18 
'3,"5Y6"2" 


54,652 
94,842 
24.786 
103,798 
22,858 
12,429 
11,607 
2,766 
27,654 
34,081 


23,310.16 

104,222.17 

19,268.18 

38,904.12 

10,790.8 

7,587.12 

6,143.17 

764.5 

22,705.13 

12,441.13 


10,659.18 


38,574.0 


1,787.17 
9,034.3 

29,679.14 

22,751.0 
2,545.19 

11,697.19 

372.17 

712.14 

6,893.3 

1,120.4 

5,254.16 

30,050.15 
6,869.19 
419.10 
2,875.0 
6,854.2 
8,689.18 
7,296.16 

26,203.18 
6,957.15 
1,040.0 

17,036.8 
9,677.15 
957.15 
6,623.14 

17,921.4 
5,587.6 
767.0 
3,873.16 
4,284.16 
1,996.8 
50.0 
3,063.8 
7,882.18 

35,669.2 


Witwatersrand  Customs  Works,  189S. 

African  Gold  Recovery 
Company. 

Rand  Central  Ore  Red. 
Company. 

Robinson  Company. 

TotaL 

Concen- 
trates. 

Tailings. 

Concen- 
trates. 

Tailings. 

Concen- 
trates. 

Tailings. 

Concen- 
trates. 

Tailings. 

463.18 

4,130.6 

9,774.7 

31,538.16 

28,335.15 

38,574.0 

35,669.2 

Gold  is  valued  at  $17  50  for  plate  gold,  and  $15  for  cyanide  gold.    (These  figures  are 
taken  from  M.  I.,  vol.  2.) 

The  table  giving  the  monthly  analysis  of  gold  production  in  the 
Witwatersrand  district,  for  April,  1894  (see  Appendix),  which  has  been 
published  by  the  Witwatersrand  Chamber  of  Mines,  will  further  illus- 
trate the  importance  of  the  cyanide  process  in  that  district. 

Cape  Colony.— In  the  British  Colony  at  the  Cape  "the  gold  mining 
industry  has  not  developed  to  such  proportions  as  to  lead  to  the  intro- 
duction of  the  cyanide  process."  (Letter  of  Secretary  of  Agriculture, 
27th  April,  1894.) 


EXEMPLIFICATION    OF    PKOCESS — THE    PROCESS    IN   AUSTRALASIA.  69 

B.    Australasia. 

(a)  New  Zealand. — A  very  successful  field  for  the  cyanide  process 
has  been  the  eminently  progressive  British  Colony  of  New  Zealand,  where 
various  classes  of  ore,  tailings  and  concentrates,  of  a  very  refractory  type, 
have  been  and  are  being  treated  on  a  large  and  commercially  successful 
scale.  The  colony  contains  the  largest  cyanide  plant  outside  of  South 
Africa,  that  of  the  Waihi  Company,  with  thirteen  vats,  where  ore  is 
treated  at  the  rate  of  2,000  tons  and  tailings  at  the  same  rate  per 
month.  The  Crown  mine  at  Karangahake  is  equipped  with  a  smaller 
but  equally  efficient  plant  for  ore  treatment.  Smaller  plants  for  treating 
ores  and  tailings  are  distributed  over  the  Hauraki  gold  fields.  An 
extensive  and  very  successful  agitation  plant  for  the  treatment  of  concen- 
trates is  connected  with  the  reduction  works  of  the  Sylvia  Company, 
Tararu,  Thames.  The  first  mine  to  adopt  the  process  has  been  the 
Crown  mine  in  the  Upper  Thames  District.  The  first  plant  was  erected 
in  an  almost  inaccessible  position  in  1889,  under  conditions  which  pre- 
cluded a  success.  New  works  have  since  been  erected  by  Mr.  MacCon- 
nell,  which  are  in  full  and  successful  operation.  The  ore  is  clean  quartz, 
with  no  sulphurets  of  base  metals;  the  free  gold  is  very  finely  divided. 
The  silver  is  in  form  of  sulphide;  some  of  the  gold  in  form  of  a  telluride. 
The  works  are  described  in  the  New  Zealand  Government  Mining  Report 
of  1893,  by  Mr.  H.  A.  Gordon,  the  Government  inspecting  engineer,  as 
follows : 

"The  ore,  when  brought  into  the  works,  is  first  dumped  onto  a  grizzly; 
what  will  not  go  through  the  bars  runs  down  to  the  rock-breaker  and  is 
broken  up  to  a  maximum  size  of  2  in.  diameter,  and  then  falls  into  the 
same  hopper  where  the  fine  material  went.  The  ore  passes  then  into 
the  drying  kilns,  which  are  built  of  brick,  the  hot  air  being  confined  in 
a  long  flue,  having  a  series  of  steps  to  prevent  the  ore  from  traveling 
down  too  fast  before  it  gets  thoroughly  dried.  There  is  a  cast-iron  plate 
at  the  bottom  of  this  flue,  which  can  be  turned  to  allow  of  the  dried  ore 
to  pass  down  into  a  large  hopper,  made  of  steel  plates,  3%  in.  thick,  from 
which  the  Challenge  ore-feeders  are  fed.  These  kilns  are  only  for  drying 
the  ore,  and  not  in  any  way  to  calcine  it.  There  are  two  of  these  kilns 
built  on  a  stone  foundation  and  placed  about  6  ft.  apart,  the  foundation 
going  all  the  way  across.  The  kilns  themselves  stand  about  30  ft.  in 
height,  the  step-flue  being  at  an  angle  of  about  30'^  to  40°  from  the 
vertical.  There  is  a  furnace  at  the  bottom,  where  either  coal  or  firewood 
can  be  used  to  dry  the  ore. 

"Stamp  Mortars. — There  is  first  a  concrete  foundation  put  in  for  the 
stamps,  and  on  the  top  of  the  concrete  the  stamp  mortars  are  placed  on 
the  end  of  a  log  of  kauri,  each  18  ft.  in  length,  4  ft.  8  in.  one  way,  and 
2  ft.  2  in.  the  other.  These  are  firmly  embedded  in  the  concrete,  and 
all  bolted  together,  so  as  to  form  a  solid  block  of  timber  standing  on 
end,  having  a  length  of  18  ft.  8  in.  by  a  width  of  2  ft.  2  in.,  and  on  this 
the  four  mortars  are  placed.  They  are  fitted  with  screens,  having  the 
top  standing  outward  at  a  slight  angle,  and  held  to  the  face  of  the  mor- 
tars by  means  of  a  long  wedge,  the  gratings  being  30-mesh,  equal  to  900 
holes  to  the  square  inch. 

"Stamps. — The  stamps  are  fitted  with  the  latest  appliances  for  raising 
and  holding  them  up,  the  cams  and  tappets  being  all  constructed  on  the 
American  type.     They  are  intended  to  make  about  ninety-two  blows 


70  THE    CYANIDE    PROCESS. 

per  minute,  having  a  drop  of  six  inches.  The  guides  and  framing  are 
made  of  wood.  Each  ten-head  battery  is  driven  by  a  separate  belt,  and 
there  is  further  provision  made  so  that  twenty  additional  stamps  can 
be  erected  should  they  at  any  time  be  required.  The  pulverized  material 
from  the  stamps  falls  into  a  chute  and  is  conveyed  into  another  set  of 
hoppers  at  a  lower  level  than  the  stamp  mortars,  and  from  these  hoppers 
the  pulverized  dust  is  taken  to  the  leaching  vats. 

*'  Cyanide  Plant. — This  consists  of  twenty-four  wooden  vats,  each  11 
ft.  long  by  9  ft.  wide,  and  3  ft.  9  in.  deep.  In  the  bottom  of  these  vats 
there  is  a  false  bottom,  or  grating,  placed  about  3  in.  above  the  ordinary 
bottom,  and  on  this  false  bottom  a  filter-bed  is  placed,  about  4  in.  in 
thickness,  the  bottom  layer  being  of  coarse  quartz-gravel  and  gradually 
getting  finer  up  to  the  top,  the  last  coating  being  fine  sand,  having  a 
coarse  cloth  placed  over  the  top  of  the  filter-bed  to  prevent  the  sand 
from  being  disturbed,  as  the  vats  get  cleaned  out  after  every  charge  of 
pulverized  ore.  There  are  also  14  agitators,  8  of  which  are  5  ft.  deep  by 
4  ft.  9  in.  in  diameter,  and  6  of  them  6  ft.  deep  and  5  ft.  6  in.  in  diameter. 
The  agitators  and  vats  are  all  made  of  kauri  timber,  the  staves  of  the 
agitators  being  3  in.  in  thickness,  and  the  vats  being  made  of  partly 
3  in.  and  partly  4  in.  timber,  and  all  bolted  together.  Into  each  of  these 
vats  are  placed  three  pipes,  under  the  false  bottom,  so  that  the  first, 
second,  and  third  solutions  can  be  drawn  off  into  separate  channels.  On 
one  side  of  each  vat  there  is  a  door,  which  can  be  opened  to  admit  of 
the  material  being  sluiced  out  after  the  whole  of  the  cyanide  solution  is 
completely  washed  out  of  the  ore,  the  solution  passing  through  a  long 
series  of  boxes  filled  with  zinc  shavings,  which  precipitate  both  the  gold 
and  silver  in  the  form  of  a  blackish  powder.  There  are  also  three 
concrete  sumps,  each  15  ft.  by  12  ft.,  and  6  ft.  deep,  capable  of  holding 
about  30  tons  of  the  cyanide  solution;  this  is  pumped  up  to  the  vats  on 
the  floor  above  as  required.  It  is  in  these  concrete  sumps  where  the 
solution  is  always  made  up  to  the  proper  strength  before  being  used. 
It  is  also  proposed  to  use  a  vacuum  pump  to  assist  the  filtration  of  the 
solution  through  the  pulverized  material  in  the  vats.  Annexed  are  plans 
of  the  company's  plant,  to  which  the  following  description  or  reference 
applies:  At  point  A,  the  ore  is  delivered  at  the  battery  and  tipped  onto 
grizzly,  B;  the  'fines'  pass  through  and  are  conveyed  to  hopper,  D; 
the  'roughs'  pass  over  the  grizzly  onto  the  stone-breaker  floor  and  are 
passed  through  stone-breaker,  C,  and  fall  into  the  hopper  underneath, 
marked  D;  the  drying- kiln,  E,  is  charged  from  this  hopper.  The  ore, 
after  passing  through  the  kiln,  being  perfectl}^  dry,  is  run  into  an  iron 
hopper,  G,  from  where  it  is  automatically  fed  into  stamps,  I,  by  self- 
feeders,  H;  the  ore,  after  passing  through  the  stamps,  is  received  in 
hoppers,  J,  and  then  conveyed  by  means  of  revolving  tube,  K,  either 
into  trucks  for  conveying  ore  to  agitation-cylinders  for  treatment,  or,  if 
the  ore  can  be  better  treated  by  percolation,  to  store-hopper,  R,  in  con- 
nection with  percolation  plant,  from  where  it  is  trucked  along  the  top 
of  and  tipped  into  percolation  tanks,  S,  for  treatment.  The  plant  is 
so  arranged  that  the  ore,  after  it  is  delivered  above  the  stone-breaker, 
passes  from  stage  to  stage  by  gravitation,  requiring  the  least  possible 
handling,  and  thereby  reducing  the  cost  of  labor  to  a  minimum. 

'^ Crushing   Machinery. — One    Lamberton    stone-breaker,    capable   of 
reducing  70  tons  of  ore  per  day  fine  enough  to  feed  into  stamps;  and 


X 

^  . 

IJ       J 

1 LT 

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*^ 

EXEMPLIFICATION    OF    PROCESS — THE    PROCESS   IN   AUSTRALASIA.  71 

20  heads  of  9  cwt.  dry  stamps,  crushing  30  tons  of  ore  per  day  through 
a  30-mesh  screen. 

"  The  Percolation  Plant  consists  of  24  tanks,  capable  of  holding  each  a 
xharge  of  7  tons  of  finely  pulverized  ore.  The  bottom  of  each  tank  is 
covered  with  a  sand  and  gravel  filter.  The  ore  is  trucked  into  the 
tanks  from  the  storage  hoppers.  A  dilute  solution  of  cyanide  is  then 
run  on  the  top,  and  allowed  or  assisted  to  percolate  through  the  body  of 
the  ore.  As  the  solution  percolates,  it  is  carried  away  from  underneath 
the  filters  by  means  of  iron  pipes,  and  permitted  to  run  through  a  series 
of  boxes  of  zinc  turnings. 

^'Agitation  Plant. — This  consists  of  sixteen  wooden  tubs,  fitted  with 
revolving  paddles,  in  which  the  ore  and  cyanide  solution  are  agitated 
together  until  the  gold  and  silver  are  dissolved.  The  pulp  is  then  fil- 
tered by  means  of  filter-presses,  and  the  bullion  deposited  from  the 
solution  on  the  zinc,  as  already  described.  The  extraction  of  bullion  is 
given  as  93  per  cent  of  the  gold  and  79  per  cent  of  the  silver  assay- value. 
The  cost  of  treatment  is  $3  50  per  ton."  This  is  the  only  company  in 
New  Zealand  which  does  not  pay  any  royalty  to  the  owners  of  the  Mac- 
Arthur-Forrest  patents,  the  patentees  owning  part  of  the  mine.  The 
total  bullion-value  produced  by  the  cyanide  process  in  these  works 
amounts  to  upward  of  $142,000. 

Another  mine  of  importance,  the  Waihi  Company,  has  recently 
adopted  cyanide  treatment  for  their  ores,  supplanting  unsatisfactory  pan- 
amalgamation.  The  ore  of  that  mine  is  very  similar  to  that  of  the  Crown 
mines.  The  bullion  recovered  by  amalgamation  has  never  exceeded  66 
per  cent  of  the  gold  and  40  per  cent  of  the  silver  assay-value.  Experi- 
ments on  a  large  scale,  made  nine  months  ago,  led  to  the  construction  of 
an  extensive  percolation  plant,  by  which  upwards  of  20,000  tons  of  ore 
have  been  already  successfully  treated.  The  extraction  varies  from  89 
to  91.8  per  cent  of  the  gold,  the  silver  extraction  from  46.5  to  51  per  cent 
of  assay-value.  The  cost  per  ton  for  cyanide  and  zinc  is  $1  37^.  The 
gold  returns  from  cyanide  treatment  are  25  per  cent  higher  than  from 
pan-amalgamation.  The  ore,  which  required  60-mesh  screens  for  amal- 
gamation, is  sufficiently  fine  for  cyanide  if  passed  through  40-mesh, 
which  means  an  increased  output  from  the  mill  of  at  least  25  per  cent, 
the  running  expenses  remaining  virtually  the  same.  Eventually  30- 
mesh  wire  gauze  may  be  used.  The  strength  of  solution  used  is  from 
0.25  to  0.4  per  cent.  The  percolation  and  subsequent  washings  can  be 
done  in  four  days.  No  difficulties  have  been  found  in  percolation,  as  the 
dry  ore  does  not  form  slimes  as  wet  ore  probably  would.  After  the  first 
percolation  is  finished,  the  subsequent  washings  are  hastened  by  atmos- 
pheric pressure  by  means  of  a  vacuum  pump.  The  extra  profit  by  cya- 
nide treatment  of  Waihi  ores  over  pan-amalgamation  amounts  to  about 
$3  75  per  ton.  The  company  has  been  experimenting  with  the  Otis 
crusher,  as  a  substitute  for  the  dry-crushing  stamp  battery;  the  results 
have  been  unsatisfactory.  A  royalty  of  7^  per  cent  on  the  bullion  pro- 
duced is  paid  to  the  owners  of  the  MacArthur- Forrest  patents,  the  Cassel 
Company  of  Glasgow.  For  the  information  in  reference  to  the  Waihi 
Company's  cyanide  operations,  I  am  indebted  to  the  company's  man- 
ager, Mr.  R.  Rose. 

A  fuller  description  of  the  working  of  the  process  has  since  been  given 
by  Mr.  Barry  in  the  report  of  Mr.  H.  A.  Gordon,  the  Inspecting  Engi- 


72  THE    CYANIDE    PKOCESS. 

neer  of  Mines  to  the  New  Zealand  Government  (New  Zealand  Mining 
Report,  1894),  as  follows: 

"  The  ore  is  first  dried  in  open  kilns,  excavated  in  tufaceous  sand- 
stone. These  are  37  ft.  deep  by  20  ft.  in  diameter  at  the  top,  and  taper 
down  to  the  bottom,  where  they  are  finished  off"  with  a  brick  arch,  having 
a  door  and  an  iron  chute  for  discharging  the  dried  ore  into  trucks. 
These  kilns  are  first  charged  with  wood  and  ore  in  layers,  each  layer  of 
wood  being  about  5  ft.  apart.  After  the  kiln  is  fully  charged,  the  wood 
is  lighted,  and  after  being  all  burned  up,  about  one  half  of  the  charge  is 
withdrawn — 50  tons — and  another  50  tons  of  raw  ore,  together  with 
wood,  added  on  the  top;  after  which  about  50  tons  is  withdrawn  every 
third  day.  This  method  of  drying  the  ore  is  found  to  be  very  economical 
as  regards  fuel,  as  there  is  not  a  large  surface  of  cold  material  to  heat 
up,  as  is  the  case  with  smaller  kilns,  which  are  emptied  at  each  charge. 
The  cost  of  firewood  used  in  large  kilns  is  37^  cents  per  ton  of  ore  dried. 
After  the  ore  is  taken  from  the  kilns,  it  is  then  put  through  the  rock- 
breaker,  from  which  it  falls  into  a  hopper,  and  thence,  by  automatic 
feeders,  it  is  fed  into  the  stamp-mortars,  when  it  is  pulverized  until  it 
passes  through  a  30-mesh  and  sometimes  a  60-mesh  screen.  It  is  in- 
tended in  the  future  to  use  a  40-mesh  standard.  As  the  pulverized  dust 
passes  through  the  screens  it  falls  into  a  narrow  trough,  when  it  is  con- 
veyed by  means  of  an  Archimedian  screw  into  a  dust-bin  at  one  end  of 
the  battery,  and  from  this  bin  the  pulverized  material  is  lifted  with  a 
bucket-belt  elevator  and  discharged  onto  an  8  in.  rubber  belt  with  rope 
edges,  and  conveyed  to  and  across  the  hopper  110  ft.  long,  running  the 
entire  length  of  the  cyanide  plant-house.  This  hopper  has  twenty  doors 
for  discharging  the  sand  into  the  trucks,  which  are  then  run  straight 
out  over  the  percolating  vats  into  travelers,  running  on  rails,  which  are 
fitted  with  hand-traversing  gearing,  enabling  a  truck  to  be  tipped  at  any 
part  of  the  vat.  This  is  an  important  point,  as  sand  has  a  tendency  to 
pack  if  moved  about  or  touched  in  any  way  after  being  tipped  into  the 
vat.  As  a  further  preventive  against  packing,  there  is  a  small  traveler 
running  under  the  main  traveler,  with  a  platform  just  at  the  height 
that  the  sand  is  to  be  filled  up  to.  All  trucks  are  tipped  over  this  plat- 
form, which  breaks  the  fall  and  throws  the  sand  olf  in  a  light  shower 
all  round.  When  the  vats  are  filled  up  to  a  depth  of  about  2  ft.,  a  strong 
solution  of  cyanide — 0.4  per  cent — is  introduced  into  the  bottom  of  the 
vat  under  the  filter-cloth,  and  forced  up  through  the  sand  until  it  stands 
about  2  in.  above  it.  The  solution  remaining  under  the  filter-cloth  is 
then  drawn  off,  and  filtration  commences;  the  2  in.  on  the  surface  taking 
about  twenty-four  hours  to  percolate  through.  After  the  whole  of  the 
strong  solution  has  been  taken  out  of  the  ore,  a  weak  stock  solution  is  run 
on  the  top  of  the  ore  to  a  depth  of  about  6^  in.  The  cock  connecting  with 
the  vacuum  cylinder  is  then  opened,  and  in  about  thirty  hours  the  sec- 
ond solution  has  passed  through;  after  which  about  10  in.  of  water  is 
run  onto  the  top,  and  when  this  has  gone  through  the  ore  the  operation 
is  completed.  The  sludge-door  in  the  vat  is  opened,  and  the  sand 
sluiced  out  by  means  of  two  2  in.  hose-pipes  under  a  head  of  150  ft. 
The  vats  are  all  circular,  22  ft.  6  in.  in  diameter,  and  4  ft.  in  depth,  of 
which  5  in.  is  taken  up  by  the  filter  bottom,  which  consists  of  a  wooden 
grating  with  edges  rounded  off  on  the  upper  side,  having  a  strong  Hes- 
sian cloth  laid  over  the  top,  which  acts  as  a  filter.  The  vats  are  made 
of  kauri  timber,  3  in.  in  thickness;  the  bottom  is  held  together  by  six, 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS   IN    AUSTRALASIA.  73 

bolts  of  f  in.  diameter.  The  staves  are  about  3  in.  in  \vidth,  joined 
close,  having  the  bottom  rebated  into  the  sides.  Each  vat  is  held 
together  by  live  round-iron  hoops,  three  of  which  are  {■  in.  and  two  1  in. 
in  diameter,  having  three  turn-buckles  on  each  hoop.  The  plant  con- 
sists of  thirteen  of  these  vats  and  two  sumps  of  the  same  diameter,  but 
6  ft.  in  depth.  Each  vat  holds  30  tons  of  ore  for  treatment;  and  it  takes 
about  four  days  to  fill  a  vat,  treat  the  ore,  and  have  it  ready  for  filling 
again.  The  precipitation  boxes  are  16  ft.  long,  2  ft.  deep,  and  17  in. 
wide,  divided  into  twelve  divisions,  of  which  the  first  and  last  are  sand 
filters,  to  clean  the  solution  going  in,  and  to  prevent  any  gold  slimes 
from  being  washed  out. 

"The  cost  of  treatment  is  being  reduced  every  month;  at  the  present 
time  it  amounts  to  about  $3  25  per  ton.  This  includes  drying,  milling, 
treatment  by  cyanide,  and  all  expenses,  except  the  royalty  paid  to  the 
owners  of  the  ^MacArthur-Forrest  patents,  from  the  time  it  leaves  the 
mine-hopper  until  the  bullion  is  in  bars." 

The  tailings  from  the  former  pan-amalgamation  process  are  being 
worked  in  a  cyanide  plant  erected  for  that  purpose  b}'  the  Cassel  Gold 
Extraction  Company.  These  works  were  completed  about  the  end  of 
February,  1894.  Mr.  H.  A.  Gordon  gives  the  following  description, 
illustrated  by  plans  which  I  reproduce:  "The  works  are  situated  in  a 
hollow  below  the  tailings  dam,  so  as  to  allow  the  tailings  to  be  run  at  a 
good  grade  into  the  percolation  vats,  and  from  there  to  be  discharged  by 
sluicing,  without  the  necessity  for  any  lifting  or  rehandling. 

"The  building  has  a  frontage  of  116i  ft.,  and  is  77  ft.  in  breadth, and 
includes  laboratories  and  oflSces,  situated  in  a  *  lean-to'  at  one  end  and 
communicating  with  the  main  building.  The  plant  consists  of  eight 
circular  percolation  vats  20  ft.  in  diameter  and  4  ft.  in  depth  (internal 
measurement),  arranged  in  two  rows,  and  having  an  intermediate  dis- 
charge-launder, toward  which  the  vats  have  a  slope  of  2  in.  to  facilitate 
the  flow  of  solutions  and  the  sluicing-out  of  residues.  All  the  vats  are 
built  of  specially  selected  and  well  seasoned  heart-of-kauri,  the  timbers 
being  3  in.  thick.  The  sides  are  hooped  with  1^  in.  iron  bolts,  connected 
and  screwed  up  by  nuts  and  cast-iron  boxes,  there  being  three  boxes  to 
each  ring.  The  bottom  planks  are  bolted  and  dowelled  tightly  together 
independently  of  the  sides.  The  filters  at  the  bottom  consist  of  a  founda- 
tion of  2  by  3  in.  slats,  9  in.  apart,  covered  by  1  in.  molding,  which 
supports  the  canvas  strainer.  This  filter  is  very  easily  laid,  and  is  most 
efiFective  in  practice.  Eech  vat  is  provided  with  a  cast-iron  door  18  by 
12  in.,  fixed  at  the  bottom  of  the  side  near  the  discharge-launder,  for 
the  sluicing  of  residues.  There  are  two  sumps  of  same  size  and  design 
as  the  percolators,  and  situated  between  the  percolators  and  front  of  the 
building,  and  on  a  sufiiciently  low  elevation.  The  sumps  are  floored 
over.  In  the  same  line  are  placed  the  reservoir  and  cylindrical  vacuum 
chamber,  13  ft.  by  3  ft.  9  in.,  under  which  latter  is  provided  a  small 
rectangular  tank,  12  ft.  by  8  ft.  by  18  in.  deep,  capable  of  holding  con- 
tents of  vacuum  chamber.  The  reservoir  is  13  ft.  9  in.  diameter  by 
5  ft.  deep  (inside  measurement),  and  is  at  such  an  elevation  as  to 
permit  solutions  to  flow  therefrom  into  percolators.  There  are  three 
extractor  boxes,  12  ft.  8  in.  by  19  in.,  with  side  discharge  for  slimes  and 
a  settler  for  cleaning-up.  The  tank  for  dissolving  the  cyanide  is  an 
iron  pan  about  3  ft.  6  in.  in  diameter  by  2  ft.  6  in.  in  height,  and  is 
capable  of  dissolving  four  boxes — i.  e.,  1,000  pounds — of  cyanide  per 


74 


THE   CYANIDE    PROCESS. 


TAILINGS     CYANIDE  WORKS   erected  by  the  CASSEL   GOLD    EXTRACTING  C?  U^  — 

—  AT  WAIHI   NZ.- 


^£r£ft£J>fC£.  . 


REFEJiESCE 

A  — Pfrcoialort. 

B~Sumpi 

C — fi€iervofr 

D—Disiohttg  Tank  /or  Cy<snt.{i. 

E —  V^ofUMm  Chamber. 

F—  Taut  to  Ffant  anient  $  of  E 

G — Zate  Exfratior  BoJUi 

H—Stmu  SeaUr. 

I—  Dtsduxrgt  Launder. 

J—  Waste  Launder. 

K — StrVng~ttqiU>r  Launder  %  t  Ht\ 

L~Atr-pvmp. 

M-Centn/ugaJ  Pmnp 

N—Petitm  Wheel  Afotor. 

O—Frtsh-valer  Supply  f'tpe* 
P—  Solulkm  Pipet,  Reservoir  to  Percolator. 

^      nt    t  m  n.       I  PercoLtttort  to 

Q-  Weai-tUptor  Ptpes  j  y^^^^^  chamber 


R—Pump  Pipes 
S—Atr-pump  Pipe. 
T —  TratKways 
U— Melting  Room 
V — Assay  Room 
W — L^iboratory. 
X—Batanee  Rdom 
Y—Dweltmg  Rmn 


.  LONGtTVDtMAL  StCTiOft  . 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS    IN    AUSTRALASIA.  75 

day.  It  is  so  arranged  that  the  requisite  amount  of  strong  solution  may- 
be run  into  the  reservoir  by  simply  turning  a  handle.  A  4  in.  centrif- 
ugal pump  serves  for  returning  the  solution  from  the  sump  to  the  reser- 
voir, and  also  an  8  in.  vacuum  pump,  which  is  capable  of  producing  a 
vacuum  of  26  in.  of  mercury.  A  line  of  pipe  runs  along  above  each 
row  of  percolation  vats,  with  a  connection  at  each  tank  for  the  hose  and 
nozzle.  One  man  can  empty  a  vat  containing  upward  of  40  tons  in 
two  hours.  A  tramway  connects  the  tailings-dams  with  the  w^orks,  and 
two  sets  of  lines  run  over  the  top  of  each  vat,  so  that  the  tailings  may 
be  equally  distributed  without  the  necessity  for  handling.  The  chief 
cliaracteristic  of  the  plant  is  its  extreme  simplicity  and  the  easy  access 
to  any  portion  of  it;  the  absence  of  any  subdivisions  or  partitions  within 
the  main  building  exposes  the  whole  of  the  plant  constantly  to  the  eye 
of  the  operator. 

"  The  system  employed  of  running  the  solutions  into  parallel  launders 
instead  of  pipes,  enables  the  solutions  from  each  vat  to  be  separately  and 
readily  sampled  and  any  mishap  may  be  at  once  detected.  The  usual 
method  of  procedure  is  as  follows:  Side-tipping  trucks  are  run  from  the 
tailings-pit  over  the  top  of  the  vat  which  is  to  be  charged.  The  contents 
of  the  trucks  are  tipped  onto  cross-bearers  resting  on  struts,  which  serve 
to  break  the  fall  of  the  tailings,  and  to  divide  them  equally  over  the 
bottom  of  the  vat.  Both  tramway  and  bearers  are  supported  entirely 
independent  of  the  vats,  so  that  no  vibrations  ma}'-  be  communicated  to 
the  latter.  A  charge  consists  of  sixty-five  truck-loads — about  33  tons, 
dry  weight — and  as  soon  as  the  vat  is  full,  '  strong '  solution — about  6 
tons  of  0.7  per  cent — is  run  onto  the  top  from  the  elevated  reservoir. 
Provision  is  made  for  either  upward  or  downward  percolation,  but  the 
latter  is  usually  adopted.  The  solution  is  now  permitted  to  gravitate 
through  the  mass  of  the  charge,  and  to  eventually  percolate  through  the 
false  bottoms  into  the  series  of  launders  in  which  it  is  conducted  to  No. 
1,  No.  2,  or  No.  3  zinc  precipitation  box,  according  to  its  strength  in 
bullion  and  cyanide.  About  twenty-four  hours  after  the  '  strong '  solu- 
tion, about  an  equal  amount  of  '  weak'  solution  (0.25  per  cent)  from  the 
sumps  is  pumped  on  and  allowed  to  gravitate.  The  residues  are  now 
washed  with  about  10  tons  of  water  in  two  charges,  which  are  rapidl}" 
drawn  off  by  suction,  and  which  displace  the  '  weak '  solution  and  leave 
the  residues  free  of  either  dissolved  bullion  or  cyanide.  The  solutions 
run  from  the  zinc  boxes  to  the  sumps,  whence  they  are  pumped  to  the 
reservoir  or  percolation  vats,  to  be  used  over  again  for  sluicing  or  weak 
solutions  as  required.  A  clean-up  of  the  gold  in  the  zinc  boxes  takes 
place  fortnightly." 

The  New  Zealand  Mining  Report  of  1893  contains  the  description  of 
an  interesting  experiment  which  was  made  some  time  ago  in  the  Waihi 
works,  with  an  apparatus  by  which  ore  was  intended  to  be  rapidly 
extracted  by  a  cyanide  solution  acting  in  a  jigging  motion  on  the  ore  in 
iron  cylinders.  The  cylinders  used  were,  however,  too  long  and  narrow, 
containing  as  they  did  some  10  ft.  in  depth  of  ore,  which  the  solution 
had  to  be  forced  through.  The  effect  of  this  was  that  the  solution  could 
not  be  made  to  percolate  through  the  whole  of  the  ore,  but  passed  up 
between  the  cylinder  and  the  ore,  the  solution  being  forced  into  the 
cylinder  by  a  pump,  at  a  pressure  of  100  lbs.  per  square  inch.  This 
pressure  should  have  been  sufficient  to  force  the  solution  through,  but 
as  the  pulverized  material  offered  greater  resistance  than  the  contact 


76  THE    CYANIDE    PROCESS. 

between  the  material  and  the  side  of  the  cylinder,  the  solution  went 
through  the  weakest  spot,  and  had  little  effect  on  the  ore.  The  process 
("the  Bohm  Process")  proved  a  failure. 

The  unquestionable  success  of  the  percolation  process  with  the  Crown 
and  Waihi  mines  has  led  to  its  adoption  by  a  number  of  other  com- 
panies which  treat  either  ores  or  tailings  by  the  process,  as  the  Te 
Komata  and  Waiorongomai  mines  at  the  Upper  Thames,  and  two  or 
three  companies  on  the  Kuaotunu  gold  field.  The  Kuaotunu  ore, 
in  which  the  gold  is  exceedingly  fine,  is  especially  adapted  for  the 
treatment,  the  only  difficulty  experienced — a  mechanical  one — is 
caused  by  the  amount  of  slimes  formed  by  some  of  the  ores,  which 
interfere  with  filtration.  The  plants  on  that  field  do  not  offer  any 
special  point  of  interest;  they  are  of  small  extent  and  give  satis- 
factory results.  The  best  one,  that  of  the  Tryfluke  Company,  will, 
however,  be  described  on  account  of  the  attempts  made  therewith  to  run 
the  tailings  direct  from  the  battery  into  the  percolation  vats.  The  plant 
consists  of  four  working  tanks,  each  12  ft.  wide,  16  ft.  long,  and  4  ft. 
deep,  having  a  filter-bed  of  3  in.  in  thickness,  covered  with  a  coarse 
cloth.  The  depth  of  ore  in  the  tanks  is  about  3  ft.  6  in.  and  about  6 
tons  of  0.25  per  cent  cyanide  solution  are  used  per  charge.  This  is 
what  is  termed  the  strong  solution.  The  tap,  which  allows  the  filtrate 
to  flow  away,  is  so  regulated  as  to  take  about  24  hours  for  that  purpose. 
After  flowing  through  six  compartments  of  a  filter  box,  which  are  filled 
with  fine  zinc-turnings,  the  solution  passes  into  a  sump,  18  ft.  long  by 
14  ft.  wide  and  4  ft.  deep,  from  where  it  is  pumped  into  the  tank  again, 
thus  forming  the  second  solution.  This  latter  is  allowed  to  filter  through 
as  fast  as  possible,  and,  after  going  through  the  boxes  filled  with  zinc, 
it  flows  into  another  sump  of  the  same  dimensions  as  that  already  men- 
tioned. The  ore  is  then  washed  with  pure  water,  after  which  the 
material  is  shoveled  out  of  the  tanks  and  run  onto  the  waste  dump. 
The  second  solution  in  the  sump,  previously  referred  to,  is  pumped  into 
a  reservoir  placed  at  a  higher  level  than  the  working  tanks.  This 
reservoir  is  10  ft.  long,  8  ft.  wide,  and  5  ft.  deep.  The  solution  is  made 
up  to  the  required  strength  before  again  being  used.  The  company  tried 
to  run  the  tailings  directly  into  the  tanks  from  the  battery,  but  they, 
like  others,  found  that  the  amount  of  slimes  in  the  ore  prevented  the 
cyanide  solution  from  filtering,  and  they  are  now  making  arrangements 
to  run  the  tailings  into  a  large  pit,  from  which  they  will  be  lifted  into 
the  cyanide  tanks.     (Extract  from  N.  Z.  Gov.  Mg.  Rep.) 

Ali  works  so  far  referred  to  are  situated  in  the  North  Island;  on  the 
large  gold  fields  of  the  South  Island  the  process  has  not  found  more  than 
experimental  application.  Experiments  have  been  made  with  gold-bear- 
ing cement  from  the  extensive  deposits  on  the  west  coast,  where  almost 
inexhaustible  quantities  of  conglomerates,  containing  black  magnetic 
oxide  of  iron  and  very  small  quantities  of  gold,  are  found.  Such  experi- 
ments were  made,  for  instance,  in  the  Reefton  School  of  Mines,  by  treating 
the  cement  in  lumps,  but  they  were  not  always  successful,  apparently  for 
mechanical  reasons.  When  the  cement  is  crushed,  a  very  good  percent- 
age is  said  to  be  extrd'cted,  the  gold  being  fine  and  well  suited  for  the 
purpose.  Tests  with  tailings  from  the  Inangahua  River  gold  fields  have 
given  good  results,  and  a  plant  for  working  a  considerable  deposit  of 
tailings  is  nearing  completion  at  Boatman's. 

The  only  instance  in  New  Zealand  where  the  agitation  system  has 


•XEMPLIFICATIOX    OF    PROCESS THE    PROCESS    IX    AUSTRALASIA. 


77 


I 


9-^ 


^^  si 
^  ilk] 

111 


S 

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78 


THE   CYANIDE    PROCESS. 


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EXEMPLIFICATION    OF   PROCESS THE    PROCESS    IN    AUSTRALASIA.  79 

been  worked  on  a  large  scale  is  in  the  works  of  the  Sylvia  Company  in 
Tararu,  Thames,  where  concentrates  of  a  very  complex  character  have 
been  treated  with  full  success  by  the  author.  The  ore  of  the  mine  named 
contains,  in  the  deeper  levels,  a  high  percentage  of  galena,  zinc-blende, 
and  copper  and  iron  pyrites.  Most  of  the  bullion  is  contained  in  the 
sulphurets  and  cannot  be  saved  by  amalgamation,  nor  is  there  any 
opportunity  for  smelting  the  sulphurets  after  concentration  or  for 
remunerative  exportation  of  the  same.  After  successful  trials  with  the 
concentrates  subjected  to  cyanide  treatment,  I  constructed  an  agitation 
plant,  of  which  I  append  my  plans,  reproduced  from  the  N.  Z.  Gov.  Mg. 
Rep.  1892.  The  concentrates  in  question  are  classed  as  jigger  concen- 
trates, first-class  slimes,  second-class  slimes,  and  huddle  concentrates. 
They  are  named  in  the  order  as  they  are  obtained  during  the  dressing 
process.  The  finest  products  contain  the  most  galena;  they  are  the 
richest  in  gold  and  silver,  and  give  the  highest  percentage  of  extraction. 
A  detailed  description  of  plant  and  extraction  process  is  given  in  the 
mining  report  above  referred  to.  I  give  here  only  the  most  salient  points: 
The  plant,  constructed  of  wood  (kauri  pine),  consists  of  three  agitators,  6  ft. 
in  diameter  by  6  ft.  in  depth;  three  Scheidel's  vacuum  filters  (patented) 
of  35  ft.  square  filter  surface  each ;  the  necessary  solution  tanks,  pipes, 
and  pumps,  and  bullion  roasting  and  melting  furnaces.  The  experience 
gained  with  this  plant,  which  works  well  with  the  exception  of  the  faults 
which  necessarily  adhere  to  the  use  of  wood  for  cyanide  plants,  induced 
me  to  construct,  later  on,  the  plant  for  the  Utica  Mine,  California,  of 
steel.  This  plant,  being  free  from  the  only  fault,  that  above  mentioned, 
answers  the  purpose  to  perfection.  The  results  of  extraction  of  the 
Sylvia  concentrates  vary  in  accordance  with  the  quality  of  the  material, 
the  slimes  giving  generally  better  results  than  the  coarser  products,  and 
the  richer  first-class  slimes  return  a  higher  percentage  of  gold  and  sil- 
ver than  the  second-class  slimes,  which  are  of  lower  grade.  Eminently 
satisfactory  results  have  been  obtained  from  the  best  slimes,  from  which 
as  high  as  96.45  per  cent  of  the  gold  and  94.59  per  cent  of  the  silver  assay- 
value  have  been  extracted.  The  average  extraction  of  100  tons  amounted 
to  86.11  per  cent  of  the  gold  and  67  per  cent  of  the  silver;  corresponding 
with  85.22  per  cent  of  the  total  value.  The  extraction  of  the  least  suited 
material,  the  jigger  concentrates,  coarse  and  low  grade,  amounted  to 
80.32  per  cent  of  the  gold  and  50  per  cent  of  the  silver.  The  average 
extraction  of  all  classes  of  concentrates  amounted  to  82.67  per  cent  of 
,the  assay- value.  The  total  amount  of  bullion  extracted  by  me  from 
about  300  tons  of  material  amounted  to  upward  of  $51,000.  The  time 
of  agitation  and  the  strength  of  solution  vary  in  accordance  with  the 
quality  of  the  material.  The  quantity  of  cyanide  used  for  the  highest 
grade  ore  amounted  to  less  than  1  per  cent,  and  for  low-grade  material 
considerably  below  0.5  per  cent  of  the  ore.  The  time  of  agitation  varied 
between  six  and  twenty-four  hours.  The  method  of  working  the  plant, 
which  permits  the  treatment  of  twenty  tons  per  twenty-four  hours,  is 
identical  with  that  of  the  Utica  plant,  which  I  propose  to  describe  in 
detail.  The  Sylvia  Company  enjoyed,  on  account  of  the  plant  being  the 
pioneer  plant  of  its  kind,  special  privileges  in  reference  to  royalty  for 
the  use  of  the  reagent. 

New  Zealand  is  among  the  few  countries,  outside  of  Africa,  where 
cyanide  treatment  of  ores,  tailings,  and  complex  concentrates  has  been 
in  all  instances  a  perfect  success.     Many  of  the  ores  of  the  Colony  are 


80 


THE    CYANIDE    PROCESS. 


particularly  suited  to  the  treatment.  Its  still  more  extensive  applica- 
tion is  prevented  by  the  royalty  charged  by  the  owners  of  the  MacArthur- 
Forrest  jjatents,  in  reference  to  which  fact  I  quote  the  Government 
Inspecting  Engineer  of  the  Colony,  Mr.  H.  A.  Gordon,  who  says  (Gov. 
Min.  Rep.  1893): 

"  There  is  no  gainsaying  the  fact  that  the  cyanide  of  potassium  is  a 
good  reagent  for  gold,  and  undoubtedly  the  best  agent  for  extracting 
gold,  especially  w^here  the  latter  is  in  a  very  finely  divided  state  among 
the  ore;  but  the  royalty  charged  is  prohibitive,  and  it  will  never  be 
largely  used  until  it  is  lowered.  If  the  Cassel  Company  (the  owners  of 
the  MacArthur-Forrest  patents)  would  have  been  content  with  about 
2  per  cent  royalty,  the  process  would  have  been  almost  universally 
adopted  by  every  company  in  New  Zealand." 

The  following  particulars  represent  the  results  of  the  working  of  the 
cvanide  process  on  the  New  Zealand  gold  fields  up  to  the  end  of  Decem- 
ber, 1893: 


Names  of  Companies. 


Bullion, 

Bullion, 

in  oz. 

value. 

15,064 

$145,930 

14,552 

51,965 

3,072 

35,895 

605 

6,410 

1,981 

4,595 

1,741 

5,155 

149 

1,1^30 

299 

2,105 

1,097 

9,045 

200 

2,255 

New  Zealand  Crown  Mines,  Karangahake,  from  ore 

Sylvia  Gold  Mg.  Co.,  Thames,  from  concentrates 

Tryfluke  Gold  Mg.  Co.,  Kuaotunu,  from  tailings 

Great  Mercur  Gold  Mg.  Co.,  Kuaotunu,  from  tailings 

Te  Aroha  Gold  Mg.  Syndicate,  Waiorongomai,  from  ore  and  tailings 

Te  Koraata  Gold  Mg.  Co.,  Upper  Thames,  from  tailings 

Red  Mercury  Gold  Mg.  Co.,  Kuaotunu,  from  tailings 

Siiverton  Gold  Mg.  Co.,  Waihi,  from  tailings 

Waihi  Gold  Mg.  Co.,  Waihi,  from  ore 

Welcome  Gold  Mg.  Tailings,  Boatman's,  from  tailings 

Totals -.- 


38,760 


$264,585 


The  returns  by  cyanide  during  the  twelve  months  ending  March  31st 
last  are:  Bullion  obtained  from  ore,  14,774  oz.;  from  tailings,  12,478  oz. 
The  year  1894  promises  to  be  even  a  more  successful  one,  six  new 
cyanide  plants  being  in  course  of  erection.  The  bullion  obtained  by 
cyanide  during  the  quarter  ending  30th  June  amounted  to  13,030  oz. 
from  ore,  and  to  7,073  oz.  from  tailings.  Fifty-two  per  cent  of  the  total 
bullion  product  in  the  North  Island  of  New  Zealand  was  produced 
during  that  period  by  the  cyanide  process. 

In  the  other  colonies  of  the  Australasian  group  the  process  is  compar- 
atively slow  in  being  introduced.  The  monetary  crisis  that  has  prevailed 
in  the  colonies,  combined  with  prejudice  and  skepticism  on  the  part  of 
the  mining  community,  have  retarded  its  introduction. 

(b)  Tasmania. — In  this  colony  the  process  has  not  yet  been  intro- 
duced on  a  working  scale.  So  far,  the  only  use  that  has  been  made  of  it, 
has  been  on  a  small  and  experimental  scale,  and  in  a  very  imperfect 
manner.  (Letter  from  Government  Secretary  for  Mines,  January  15, 
1894.) 

(c)  Western  Australia. — Here  the  process  has  not  been  adopted  on 
a  large  scale,  "the  mining  industry  being  yet  in  its  infancy.  The 
process  is,  however,  considered  the  best  known  for  Western  Australian 
gold  ores,  and  some  minor  experiments  have  been  made  with  tailings, 
giving  good  results."  (Letter  from  Government  Secretarv  of  Mines, 
January  19,  1894.) 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS   IN   AU^RALASIA.  81 

(d)  South  Australia. — This  colony  has  several  plants  for  the  work- 
ing of  the  cyanide  process,  one  of  which,  that  at  Mt.  Torrens,  is  being 
worked  as  a  custom  works  by  the  Mines  Department  of  the  State  for 
the  purpose  of  giving  the  mine  owners  an  opportunity  to  have  their 
ores  tested.  A  Government  plant  undoubtedly  inspires  miners  and 
prospectors  with  confidence.  A  charge  just  sufficient  to  cover  cost  of 
treatment  is  made  by  the  department. 

"  The  plant  has  now  been  in  operation  for  some  weeks,  and  the  treat- 
ment of  an  ore  parcel  from  the  Blacksnake  Mine  has  been  completed. 
The  ore  contained  on  an  average  16  dwts.  15  grs.  of  gold;  of  this,  10  dwts. 
8  grs.  were  saved  by  the  battery,  4  dwts.  9  grs.  by  cyanide,  leaving  1 
dwt.  and  22  grs.  in  the  tailings.  The  ore  contained  quartz,  hematite, 
and  about  4  per  cent  of  iron  pyrites."  (Letter  from  Secretary  for  Crown 
Lands,  May  23,  1894.) 

A  plant  for  treating  500  tons  per  month  is  at  work  on  tailings  at  the 
Virginia  Gold  Mining  Company's  property,  and  is  doing  good  work. 
The  tailings  from  the  battery  are  allowed  to  dry,  and  are  then  trucked 
into  vats  of  a  capacity  of  between  25  to  30  tons,  16  ft.  in  diameter  by  5 
ft.  in  depth.  The  sumps  are  built  of  cement,  16  ft.  by  14  ft.  by  12  ft. 
The  consumption  of  cyanide  is  about  1^  lbs.  per  ton  of  tailings.  The 
tailings  before  treatment  assay  from  10  to  15  dwts.,  after  treatment,  1 
dwt.  7  grs.  per  ton.  The  bullion  is  refined  with  nitre.  The  vats  are 
charged  twice  a  week,     (GovernJhent  letter.) 

(e)  Queensland. — At  Charters  Towers,  a  plant  capable  of  treating 
800  tons  per  month  has  been  erected  by  the  Australian  Gold  Recovery 
Company,  Lim.,  the  owners  of  the  MacArthur-Forrest  patents  for  Aus- 
tralia, from  which  the  following  information  has  been  obtained:  It 
is  a  custom  plant.  The  chief  material  treated  is  sludges,  which  are 
purchased  from  the  surrounding  mills  in  varying  quantities.  These 
sludges  are  concentrates  which  have  been  submitted  to  fine  grinding 
and  amalgamating  in  berdans;  this  material  is,  if  necessary,  mixed 
with  coarse  sand  or  tailings,  and  treated  by  percolation;  vacuum  pumps 
are  used  to  assist.  Difierent  classes  of  ore  of  a  refractory  character  are 
treated  in  the  works,  and  the  conditions  of  treatment  are  varied  with 
the  character  of  the  ore.  Operations  were  started  in  August,  1892,  since 
which  date  about  9,200  tons  of  sludges  have  been  treated,  with  a 
return  of  9,633  oz.  of  gold.  "At  Croydon  a  tailings  plant  has  been 
erected  at  the  Cumberland  property  of  a  capacity  of  1,500  tons  per 
month.  Plants  for  the  treatment  of  2,000  and  1,000  tons  per  month 
are  in  course  of  erection  for  the  Croydon  Quartz  Crushing  Company  and 
the  Pioneer  Gold  Mining  Company,  respectively."  (Australian  Gold 
Recovery  Company.) 

(f)  New  South  Wales. — In  this  colony  the  cyanide  process  is  at 
work  only  at  the  Mitchell's  Creek  gold  mine,  where  the  plant  and 
operations  are  described  by  Mr.  James  Taylor,  the  Government  metal- 
lurgist, as  follows:  "The  works  have  been  erected  for  the  treat- 
ment of  a  dump  of  old  tailings  estimated  to  contain  about  18,000  tons, 
and  found  by  careful  sampling  to  contain  8  dwts.  4  grs.  of  gold  and 
11  dwts.  10  grs.  of  silver  per  ton.  The  plant  consists  of  two  400- 
gallon  iron  tanks,  two  storage  vats,  six  percolating  vats,  two  sets  of 
ten  precipitating  boxes,  two  sumps,  iron  pipes  for  conveying  the  solu- 

6cp 


82  '  THE    CYANIDE    PROCESS. 

tions  and  washes,  side-tipping  wagons  and  tram-rails  for  charging  and 
discharging  the  percolating  vats,  steam  boiler  and  pump  to  return  the 
cyanide  solution  from  the  sump  to  the  storage  vat,  small  muffle  furnace 
for  roasting  the  precipitated  gold  with  its  admixture  of  zinc  and  copper, 
laboratory  and  assay  furnaces. 

"In  the  two  iron  tanks  the  cyanide  stock  solution  is  prepared  by  dis- 
solving crude  potassium  cyanide,  suspended  in  a  wire  gauze  tray  in 
water.  The  crude  salt  contains  about  75  per  cent  of  pure  potassium 
cyanide,  and  the  stock  solution  is  made  up  to  a  strength  of  from  10  to 
25  per  cent.  From  the  iron  tanks  the  solution  is  run  through  a  canvas- 
bottomed  box,  which  serves  as  a  filter,  into  one  or  the  other  of  two  storage 
vats,  as  it  is  needed  to  bring  up  the  strength  of  the  returned  liquor  to 
the  standard  required  for  the  treatment  of  the  next  charge  of  ore,  say 
about  0.7  per  cent  of  cyanide.  These  two  wooden  storage  vats  are  16  ft. 
in  diameter  and  5  ft.  deep,  and  are  placed  sufficiently  high  to  discharge 
into  the  next  series  of  vats  by  means  of  iron  pipes.  The  six  large 
percolating  vats,  each  18  ft.  in  diameter  and  5  ft.  deep,  are  provided 
with  filter-bottoms,  built  up  by  laying  ribs  of  Avood,  notched  on  the 
under  side,  along  the  bottom  of  the  vat  at  regular  intervals.  On  these 
ribs  is  spread  cocoanut  matting,  and  over  this  comes  a  layer  of  wool- 
pack.  The  edges  of  the  filtering  cloths  are  well  caulked  along  the  sides 
of  the  vat.  The  vats  are  charged  with  tailings  by  means  of  side-tipping 
wagons,  carried  on  an  over-head  tram-line,  and  the  exhausted  tailings 
are  discharged  by  being  shoveled  through  an  18  in.  hole  in  the  side  of 
the  vat,  near  the  bottom,  into  a  wagon  running  on  rails  and  leading  to 
the  waste  dump.  Each  percolation  vat  receives  a  charge  of  35  tons  of 
tailings,  and  two  vats  are  emptied  and  refilled  daily  during  the  day 
shift,  so  that  70  tons  of  tailings  are  treated  every  twenty-four  hours. 
The  fresh  charge  of  tailings  is  first  soaked  with  returned  solution,  which 
begins  to  make  its  appearance  at  the  bottom  of  the  vat  in  about  three 
hours  from  the  time  of  its  application.  A  solution  of  0.7  per  cent  is 
then  turned  on,  and  this  is  allowed  to  act  for  about  twenty-five  to  thirty 
hours;  it  is  then  drawn  off,  running  direct  to  the  precipitating  boxes. 
About  twenty  inches  of  liquid  from  the  storage  vat  is  sufficient  to  soak 
the  charge,  and  a  similar  amount  of  the  reinforced  solution  is  enough 
for  the  gold  extraction,  after  the  application  of  which  water  is  run  on  to 
wash  out  the  cyanide  solution.  Each  of  the  percolation  vats  can  be 
supplied  with  cyanide  solution  from  the  storage  vats  by  means  of  a 
21  in.  pipe,  and  with  water  through  a  2  in.  pipe,  for  washing  after  the 
cyanide  solution  has  been  drained  off,  or  before  the  cyanide  solution  has 
been  added  should  that  be  found  necessary,  as  is  sometimes  the  case. 
The  tailings  are  under  treatment  in  the  vat  during  a  period  of  about 
sixty-four  hours  from  the  completion  of  charging  to  the  commencement 
of  discharging  the  vats. 

"An  inch  and  a  half  pipe  proceeding  from  the  bottom  of  the  percolat- 
ing vats  takes  the  gold  solution  to  the  precipitating  boxes,  where  the 
liquid  is  caused  to  pass  upward  successively  through  a  series  of  ten 
boxes,  filled  with  fine  zinc  turnings,  made  on  the  spot  from  the  zinc  lin- 
ings of  the  boxes  in  which  the  potassium  cyanide  has  been  imported. 
The  gold  and  silver  are  precipitated  upon  the  zinc  as  a  fine  black  slime, 
accompanied  by  any  copper  that  may  have  been  taken  up  by  the  solution 
from  the  tailings.  After  passing  these  boxes,  the  solution,  almost  or 
altogether  free  from  gold,  is  collected  in  a  couple  of  sumps,  each  16  ft.  in 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS    IN    AMERICA.  83 

diameter  and  5  ft.  deep,  from  which  it  is  pumped  back  to  the  storage 
vats,  ready  for  another  application,  either  for  soaking,  or,  when  suitably 
reinforced,  for  gold  extraction.  When  a  clean-up  is  being  made,  the  zinc 
in  the  boxes  is  well  stirred  to  shake  off  the  slimes,  which  are  then  washed 
out  through  a  plug-hole  into  a  launder,  where  they  are  collected,  and 
either  roasted  and  melted  with  a  little  flux,  or  treated  with  acid  and 
then  melted;  the  mode  of  procedure  depends  upon  the  amount  of  base 
metal  mined  with  the  gold  and  silver.  All  solutions  going  from  the  per- 
colating vats  pass  through  the  precipitating  boxes,  excepting  of  course 
the  wash  water  retained  as  moisture  in  the  tailings  when  the  vat  is  emp- 
tied. The  tailings  contain,  as  noted,  8  dwts.  of  gold  and  11  dwts.  10  grs. 
of  silver  to  the  ton.  The  returns  for  a  recent  run  of  ten  weeks  show 
that  64  per  cent  of  the  gold  and  about  the  same  of  silver  was  actually 
recovered;  but  by  assay  of  the  tailings  after  treatment  it  appears  that 
70  per  cent  of  the  gold  had  been  removed;  hence  something  like  6  per 
cent  seems  to  be  locked  up  in  the  plant,  and  may  be  obtained  later. 
The  cost  of  cyanide  during  the  same  period  of  ten  weeks  amounted  to 
$2  58  per  ton  of  tailings,  and  the  total  cost  of  treatment  to  $3  38  per 
ton.  The  tailings  contain  from  0.25  per  cent  to  0.50  per  cent  of  copper, 
the  presence  of  which  increases  the  amount  of  cyanide  used  by  from  75 
cts.  to  $1  per  ton,  and  further  acts  injuriously,  as  it  is  precipitated  by 
the  zinc  with  the  gold  and  silver  and  debases  the  bullion  obtained,  thus 
necessitating  refining  operations.  The  force  employed  in  the  works 
consists  of  one  scientific  manager,  two  men  on  alternate  twelve-hour 
shifts  to  attend  to  the  circulation  of  the  solutions,  nine  men  to  fill  and 
empty  the  vats,  one  man  to  prepare  the  cyanide  solution  and  to  do  odd 
jobs,  and  a  laboratory  boy.  The  cost  of  the  plant  was  approximately 
$10,000;  it  was  erected  under  the  auspices  of  the  Australian  Gold  Recov- 
ery Company,  Limited"  (MacArthur-Forrest  patents).  During  six 
months  9,972  tons  have  been  treated,  with  an  extraction  of  2,512  oz.  of 
gold. 

(g)  Victoria. — "A  plant  of  2,000  tons  per  month  is  being  constructed 
at  the  New  Golden  Mountain  Gold  Mining  Company's  property,  and  it 
is  proposed  to  treat  the  ore  at  these  works  directly  by  cyanide,  without 
any  previous  treatment  or  battery  amalgamation".  (The  Australian 
Gold  Recovery  Compan3^) 

C.    The  United  States  of  America. 

The  introduction  of  the  cyanide  process  in  the  United  States  as  a 
metallurgical  process  on  a  commercial  basis  has  so  far  been  slow;  the  ter- 
ritory is  vast,  the  mining  districts  are  widely  scattered,  and  there  is  an 
almost  invincible  prejudice  against  any  new  process,  particularly  patent 
processes,  owing  to  the  innumerable  failures  in  which  for  years  past 
much  money  has  been  lost.  Of  late  the  process  has  been  tested  on 
many  ores  from  almost  all  mining  camps  in  the  United  States.  It  has 
been  found  successful,  on  a  small  scale,  in  many  instances.  Its  tech- 
nical application  has,  however,  not  always  been  the  expected  success,  for 
which  fact  various  causes  are  responsible.  In  many  instances  plants 
have  been  erected  where  either  the  ore  is  unsuited  for  the  process  or 
where  the  supply  of  suitable  ore  is  insufficient;  in  other  instances  the 
working  of  the  process  has  been  intrusted  to  incompetent  hands,  which 


84  THE   CYANIDE    PROCESS. 

naturally  led  to  a  failure.  The  Mac  Arthur-Forrest  patents  and  the 
Simpson  patent  are  owned  in  the  United  States  by  the  Gold  and  Silver 
Extraction  Company  of  America,  Lim.,  of  Denver.  A  number  of  extrac- 
tion works  have  been  erected  all  over  the  United  States  by  mining  com- 
panies and  other  parties.  To  obtain  reliable  information  of  their  results 
and  their  plants  has  proved  possible  only  in  a  few  instances,  and  it  is 
hardly  possible  to  form  from  such  information  an  adequate  idea  about 
the  success  of  the  process  in  this  country. 

(a)  Utah. — The  first  mill  to  operate  cyanide  treatment  in  this  Terri- 
tory is  owned  by  the  Mercur  Gold  Mining  and  Milling  Company.  That 
company  had  just  completed  a  pan-amalgamation  plant  at  a  cost  of 
$30,000,  which  proved  a  failure,  only  20  per  cent  of  the  gold  being 
recovered,  when  small  tests  with  cyanide,  followed  by  good  results,  led 
to  the  introduction  of  the  process  on  a  large  scale,  which  has  since  proved 
a  full  success.  For  the  following  description,  by  Louis  Janin,  Jr.,  I  am 
indebted  to  the  Engineering  and  Mining  Journal  (Oct.  7,  1893): 

"  The  ore  passes  through  a  Dodge  rock-breaker,  and  is  crushed  by  two 
sets  of  Wall's  corrugated  rolls;  the  first  are  set  to  one  half  inch,  the 
second  to  one  quarter  inch.  This  very  coarse  ore  (over  20  per  cent  of 
the  product  which  goes  to  the  leaching  vats  does  not  pass  a  half-inch 
mesh)  is  treated  by  C3^anide  percolation.  The  dimensions  of  the  vats 
are  12  ft.  8  in.  diameter;  depth  to  false  bottom,  35  in.;  giving  a  capacity 
of  about  fourteen  tons  when  the  vats  are  filled  to  within  6  in.  of  the 
top.  In  consequence  of  the  crudeness  of  the  crushing,  the  time  of 
leaching  varies  greatly;  it  occupies  between  ten  and  two  hundred 
and  forty  hours.  It  is  claimed  that  the  ore  (which  is  a  silicious  sur- 
face-ore with  the  gold  finely  divided)  is  singularly  constant  in  value 
and  quality;  the  wide  differences  in  the  time  of  treatment  are  ascribed 
to  the  differences  in  mechanical  condition.  As  a  rule,  the  cyanide  solu- 
tion is  left  standing  with  the  ore  for  twelve  hours;  it  is  then  passed 
through  continuously,  until  practically  all  gold  is  extracted;  the  time 
required  varies  from  thirty-six  to  forty-eight  hours.  The  percolation 
liquor  passes  through  zinc  boxes  40  ft.  long,  and  is  returned  to  the  stock 
solution  tank,  where  its  proper  strength  is  made  up  again  by  addition  of 
cyanide.  After  the  ore  in  the  tank  has  been  leached  sufficientl}^,  the  tank 
is  allowed  to  drain.  However,  a  considerable  quantity  of  solution,  about 
400  lbs.  to  the  ton,  or,  with  the  0.25  per  cent  solution  used,  about  1  lb. 
potassium  cyanide  to  the  ton  of  ore,  remains  in  the  vat.  To  dislodge 
this,  wash  water  is  used,  either  plain  water  or  sometimes  a  weak  solu- 
tion resultant  from  washing.  In  the  latter  case,  the  weak  solution  is 
stored  in  separate  tanks,  and  this  arrangement  allows  washing  with  a 
minimum  wastage  of  solution.  The  extraction  of  the  Mercur  ore  has 
varied;  at  the  beginning  of  operations  it  was  considerably  below  70  per 
cent,  but  as  experience  with  the  process  increased  the  results  became 
better;  the  average  is  now  given  as  between  85  and  90  per  cent.  The  cost 
of  treatment  during  an  early  period  of  the  work  is  given  at  $2  40  per 
ton,  divided  as  follows:  Potassium  cyanide  (1.27  lbs.  per  ton),  66  cts. ; 
zinc  (0.55  lb.  per  ton),  5  cts.;  labor  (seven  shifts  per  twenty-four  hours, 
6  day  and  1  night),  $1  12;  supplies,  repairs,  fuel,  and  freight,  57  cts.; 
total  (not  including  ofiice  expenses,  royalty,  and  superintendence), 
'$2  40.  Since  that  period,  the  expenses  have  been  reduced  as  the  amount 
of  cyanide  lost  per  ton  of  ore  has  been  diminished,  and  a  larger  quan- 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS   IN    AMERICA.  85 

tity  of  ore  is  reduced  with  the  same  amount  of  hxbor.  Comparative 
results  by  actual  experience  on  the  ore  by  amalgamation  and  cyanide 
treatment  are  as  follows:  1,500  tons  of  ore  treated  by  amalgamation 
gave  an  average  extraction  of  20  per  cent  at  a  cost  of  $4  25  per  ton  for 
milling;  1,600  tons  of  ore,  treated  during  90  days  by  cyanide,  averaged 
an  extraction  of  88.5  per  cent,  at  a  cost  of  $2  25  for  milling."  The  intro- 
duction of  the  cyanide  process  has  made  the  Mercur  Company  a  remark- 
able financial  success;  it  paid  during  the  first  five  months  of  this  year 
$150,000  in  dividends.  The  plant  is  being  increased  to  a  capacity  of 
250  tons  per  day. 

(b)  Montana. — One  of  the  first  cyanide  mills  in  this  State  was 
erected  by  F.  B.  &  R.  B.  Turner,  in  Revenue,  Madison  County,  who 
supplied  the  information  which  follows:  The  gold  in  the  Revenue 
ores  has  always  been  very  hard  to  save,  the  best  amalgamation 
methods  only  saving  from  25  to  27  per  cent  of  the  assay-value;  the 
application  of  the  cyanide  process  increases  the  returns  to  from 
80  to  87  per  cent.  Extensive  tests  have  proved  that  the  wet-crush- 
ing and  cyanide  treatment  is  profitable  only  on  low-grade  ore,  as 
the  loss  of  low-grade  slimes  connected  with  that  method  is  consid- 
ered immaterial.  The  most  successful  treatment  with  cyanide  has 
been  found  to  be  percolation  of  dry-crushed  ore.  The  present  plant  (see 
diagram,  p.  86)  is  used  for  wet-crushing  of  low-grade  ore.  The  tailings 
from  the  battery  pass  into  settling  pits,  and  the  slimes  are  allowed  to  flow 
into  a  large  reservoir  below  the  mill  for  eventual  future  treatment.  The 
tailings  settled  in  the  pits  are  shoveled  into  the  leaching  tanks;  the 
running  of  the  pulp  direct  into  the  percolation  vats  proved  here,  like  in 
many  other  localities,  a  failure,  owing  to  the  slimes.  A  dry-crushing 
plant  of  25  tons  per  day  is  now  in  course  of  construction  (see  diagram); 
after  its  completion,  ores  of  about  $25  value  will  be  crushed  in  the  dry, 
poorer  ores  in  the  wet  mill.  The  Revenue  ore  is  nearly  pure  silica,  con- 
taining from  1  to  2  per  cent  of  iron  peroxide  and  no  sulphurets.  It  is 
crushed  and  passed  through  a  30-mesh  steel  screen.  Some  of  the  per- 
colation vats  are  of  10  ft.  diameter  by  a  depth  of  4^  ft.,  others  are  of 
12  ft.  diameter  by  4  ft.  deep;  they  are  made  of  3-in.  Oregon  pine.  The 
strength  of  the  solution  varies  from  0.6  to  1  per  cent;  percolation  takes 
from  24  to  36  hours,  after  which  the  solution,  which  is  circulated  or 
pumped  back,  varies  from  0.4  to  0.8  per  cent  of  cyanide.  One  half  ton 
of  solution,  on  an  average,  is  used  for  treating  one  ton  of  ore.  The  total 
extraction  amounts  to  from  80  to  87  per  cent  of  the  assay-value  of  the 
ore,  27  per  cent  of  which  is  obtained  from  amalgamation  on  the  plates. 
Cyanide  extracts  from  73  to  79  per  cent  of  the  value  left  in  the  tailings 
after  amalgamation.  No  difficulty  is  being  experienced  in  precipitating 
the  gold.  The  consumption  of  zinc  amounts  to  about  half  a  pound  per 
ton  of  ore.  Sulphuric  acid  is  used  for  bullion  refining;  the  fineness  of 
melted  bullion  is  from  920  to  940.  The  total  cost  of  treatment  amounts 
to  $5  per  ton,  including  $1  patent-royalty,  and  consists  of  the  following 
items:  Crushing  and  labor,  $2;  chemicals,  $2;  patent-royalty,  $1.  The 
actual  consumption  of  cyanide  is  from  2^  to  3  lbs.  per  ton  of  ore.  The 
total  cost  of  the  plant  amounted  to  about  $20,000,  including  engines, 
boilers,  stamps,  and  vats,  all  placed  in  position.  Eight  to  ten  men  are 
employed  in  the  mill. 

A  cyanide  mill   erected  by  the   Henderson   Mountain    Mining   and 


86 


THE    CYANIDE    PROCESS. 


Milling  Company,  near  Cooke,   Park  County,  was  worked  on  surface 
hematite  ore  for  some  time  with  fairly  satisfactory  results. 


(c)  Colorado. — The  owners  of  the  Mac  Arthur-Forrest  patents  possess 
a  small  plant  for  testing  ore  parcels  in  South  Denver. 

The  Cripple  Creek  Gold  Extraction  and  Power  Company  erected  a 
plant  in  Cripple  Creek,  in  reference  to  which  I  received  the  following 
communication  from  the  technical  manager  (Mr.  J.  K.  Turner): 

"A  small  plant  has  been  a  remarkable  success,  and  an  addition  to  it 
is  now  in  course  of  erection,  bringing  its  capacity  up  to  50  tons  daily. 
The  machinery  will  finally  consist  of  three  Gates'  crushers,  two  pulver- 


EXEMPLIFICATION    OF    PROCESS THE    PROCESS    IN    AMERICA.  8/ 

izers,  four  screens,  four  iron  leaching  vats  of  20  ft.  diameter,  two  solution 
tanks  of  15  ft.  diameter,  and  four  zinc  boxes  of  40  ft.  length.  The  plant 
is  running  as  a  custom  mill,  and  many  classes  of  ore  are  being  treated; 
at  present  about  30  tons  per  day.  The  ore  is  crushed  dry  and  passed 
through  a  20-mesh  screen.  The  cyanide  solution  used  is  0.75  per  cent,  the 
strength  of  which  is  by  percolation  reduced  to  0.5  per  cent.  One  half 
ton  of  solution  is  required  for  the  treatment  of  one  ton  of  ore.  The 
extraction  of  gold  averages  90  per  cent,  that  of  silver  84  per  cent.  Sul- 
phuric acid  is  used  for  bullion  refining;  the  bullion  is  from  775  to  790 
fine.  Copper  and  zinc  compounds  in  some  ores  have  been  found  to 
interfere  with  extraction.  The  average  value  of  the  ore  is  $30  before 
and  $3  after  cj^anide  treatment.  The  cost  of  treatment  amounts  to  $4  70 
per  ton.  The  cost  of  the  plant  was  $20,000.  Seven  men  are  employed 
in  the  works." 

The  successful  cyanide  treatment  of  Cripple  Creek  ores,  as  here  de- 
scribed, is  very  interesting,  for  the  ores  in  that  district  contain  a  large 
amount  of  telluride  minerals.  Many  ores  contain  sylvanite,  krennerite, 
and  calaverite. 

The  Puzzler  Gold  Mining  and  Milling  Company  of  Denver  have 
ceased  to  work  their  cyanide  plant  at  Ward,  Boulder  County,  although 
they  were  successful  with  the  process. 

A  cyanide  plant  at  Junction  Creek  is  reported  in  successful  operation. 
(M.  S.  P.) 

(d)  Nevada. — A  branch  company  was  formed  by  the  owners  of  the 
MacArthur-Forrest  patents  for  introducing  the  cyanide  process  on  the 
Comstock  Lode.  A  number  of  laboratory  experiments  made  in  the  Con. 
Virginia  and  California  Company  did  not  lead  to  the  adoption  of  the 
process. 

(e)  Arizona. — No  information  can  be  obtained  in  reference  to  the 
process  in  this  Territory,  where  a  company  has  been  organized  for  its 
introduction,  with  the  exception  of  that  obtained  from  the  Champies 
Mine,  Yavapai  County,  where  the  results  were  unsatisfactory,  appar- 
ently on  account  of  faulty  technical  manipulation. 

(f)  New  Mexico.— The  Deep  Down  Mine  had  adopted  the  cyanide 
process,  but  abandoned  it  in  favor  of  pan-amalgamation,  the  reasons 
for  which  are  explained  (Engineering  and  Mining  Journal)  as  consist- 
ing in  a  change  of  the  character  of  the  ore. 

(g)  South  Dakota.— The  Black  Hills  Gold  and  Silver  Extraction 
Mining  and  Milling  Company  of  Deadwood  have  of  late  erected  a  cyanide 
plant,  about  which  the  general  manager,  Mr.  I.  S.  Childs,  gives  the  fol- 
lowing details: 

"  The  ore  consists  of  from  80  to  95  per  cent  of  silica,  accompanied  by 
variable  quantities  of  iron,  both  in  the  form  of  peroxide  and  the  various 
■conditions  of  partial  oxidation,  and  contains  traces  of  copper,  manganese, 
arsenic,  and  antimony.  The  ore  is  dry-crushed  with  rolls,  and  passes 
through  a  30-mesh  screen.  The  percolation  vats  of  steel  are  24  ft.  in 
diameter  by  3  ft.  in  depth.  The  cyanide  solution  is  usually  of  0.5  per 
cent  strength;  its  quantity  amounts  to  half  the  weight  of  the  ore.  From. 
85  to  90  per  cent  of  the  assay-value  in  gold  and  from  50  to  75  per  cent 


88  THE    CYANIDE   PROCESS. 

of  the  silver  value  is  extracted.  All  extracted  bullion  is  recovered. 
Lime  is  used  with  the  ore  and  caustic  soda  with  the  concentrates  to 
remedy  the  'acidity.'  The  consumption  of  zinc  amounts  to  0.55  lb.  per 
ounce  of  bullion  recovered.  The  treatment  takes  from  twenty-four  to 
forty-eight  hours.  The  value  of  the  material  before  treatment  is  $20; 
the  tailings  assay  from  $2  to  $3  in  gold.  The  total  expenses  for  treat- 
ment, including  $1  patent-royalty,  are  $3  50  per  ton.  The  plant  for  the 
treatment  of  40  tons  per  twenty-four  hours  cost  $25,000.  Fifteen  men 
are  employed  per  twenty-four  hours." 

The  Golden  Reward  Chlorination  Works,  of  Deadwood,  are  reported 
as  adding  cyanide  works  to  their  plant.     The  works  ar,e  custom  works. 

Many  tests  with  cyanide  have  been  made  in  various  other  States,  in 
some  instances  leading  to  the  adoption  of  the  process  on  a  commercial 
scale;  in  others,  experiments  were  conducted  with  little  knowledge  and 
in  a  cursory  manner;  in  other  instances,  again,  the  character  and  quali- 
ties of  the  ore  prevented  cyanide  treatment  from  being  a  success.  One 
instance,  where  the  process  was  first  used  but  afterwards  abandoned,  is 
the  Creighton  Mining  and  Milling  Company,  Cherokee  County,  Georgia, 
where  the  extraction  from  concentrates  from  old  oxidized  tailings,  as 
described  by  the  general  manager,  was  reasonably  good,  being  82  per 
cent  of  the  assay-value;  from  the  fresh  concentrates  from  deeper  levels, 
however,  the  returns  were  only  50  per  cent,  in  consequence  of  which  the 
process  was  discarded  and  barrel  chlorination  introduced  in  its  place 
(H.  T.  Fisher).  In  other  instances  the  value  of  the  ore  in  the  mine  fell 
off,  so  that  not  only  the  cyanide  process,  but  all  operations  had  to  be 
stopped.  An  instance  in  point  offers — the  Moratock  Mine,  Montgomery 
County,  North  Carolina.  The  engineer  in  charge  stated  (Engineering 
and  Mining  Journal)  that  he  had  no  trouble  in  treating  the  ores  of  that 
mine  by  cyanide  and  making  a  high  extraction  (95  per  cent)  at  a  mod- 
erate cost.  Cyanide  solution  of  0.25  per  cent  was  used;  the  total  cost  of 
mining,  milling,  and  royalty  amounted  to  about  $3  75.  The  mine, 
however,  was  shut  down,  the  ore-value  receding  to  $1  25. 

(h)  California. — The  Shasta  Gold  Recovery  Company  erected  a  mill 
under  the  direction  of  Mr.  A.  B.  Paul.  The  mill  has  been  working  for 
some  time  successfully.  Mr.  Paul  was  one  of  the  first,  if  not  the  first, 
who  used  wet-crushing  of  the  ore  with  cyanide  solution,  instead  of  water, 
in  the  mortars.  No  authentic  information  could  be  obtained  in  refer- 
ence to  his  results. 

A  cyanide  plant  has  been  erected  at  the  Gold  Run  Mine,  Siskiyou 
County,  the  working  of  which  has  been  described  in  the  California 
Mining  Report,  No.  11,  page  430. 

The  following  information  referring  to  the  cyanide  process  in  Kern 
County,  has  been  contributed  by  Mr.  W.  L.  Watts,  assistant  in  the  field 
to  the  California  State  Mineralogist:  "A  company  which  was  organized 
in  St.  Louis  to  reopen  the  Bright  Star  Mine  in  Kern  County,  attempted 
to  work  several  thousand  tons  of  tailings  at  that  mine  by  the  cyanide 
process.  It  is  said  that  the  leaching  plant  used  for  the  purpose  could 
only  handle  six  tons  of  tailings  every  twenty-four  hours,  and  that  about 
45  per  cent  of  the  precious  metal  was  recovered." 

"  The  Cyanide  Process  at  Havilah,  Kern  County. — In  1892,  Meesi-s. 
Stebbins  and  Porter  commenced  leaching  at  Havilah.    They  first  treated 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS   IN    CALIFORNIA.  89 

50  tons  of  heavy  sulphuretted  concentrates  at  the  Reese  mill.  The  assay- 
value  of  these  sulphurets  ranged  from  $15  to  $48  per  ton.  Owing  to 
leakage  and  other  causes,  their  first  experiments  were  not  remunerative, 
but  the  last  and  richest  portion  of  this  batch  of  concentrates  was  treated 
with  great  success,  86  per  cent  of  the  precious  metal  being  saved.  One 
difficulty  encountered  arose  from  the  fact  that,  owing  to  the  sulphurets 
having  long  been  exposed  to  the  air,  they  were  partially  oxidized  into 
acid  sulphates;  the  detrimental  effect  of  these  sulphates  was  eventually 
overcome  by  neutralizing  them  with  quicklime.  One  hundred  tons  of 
tailings  were  then  treated  at  the  Hayes  mill.  These  tailings  showed  an 
assay-value  of  $20  per  ton,  and  about  91  per  cent  of  the  precious  metal 
was  saved.  This  last  lot  of  tailings  consumed  3  lbs.  of  potassium 
cyanide  to  the  ton  of  ore.  The  process  employed  is  as  follows:  The 
tailings  are  first  treated  in  a  tank  6  ft.  long,  6  ft.  wide,  and  6  ft.  deep, 
and  holding  a  charge  of  six  tons  of  ore.  In  this  tank  the  tailings  are 
saturated  with  a  solution  containing  one  half  of  one  per  cent,  by  weight, 
of  potassium  cyanide.  The  tailings  are  allowed  to  stand  in  this  solution 
for  forty-eight  hours,  and  are  then  sluiced  into  'filter-bottom  tanks,' 
where  they  are  washed.  These  'filter-bottom  tanks'  are  7  ft.  long,  10 
ft.  wide,  and  3  ft.  deep.  The  tailings  are  sluiced  from  the  saturating  tank 
with  a  stock  solution  which  has  a  strength  of  one-fifteenth  of  one  per 
cent  of  potassium  cyanide.  About  1,000  gallons  of  stock  solution  are 
used  in  sluicing  six  tons  of  ore.  The  filtrate  is  then  tested  to  determine 
whether  a  sufficient  percentage  of  the  gold  and  silver  value  of  the  pulp 
(as  shown  by  assay)  has  been  dissolved.  If  the  filtrate  is  found  to  con- 
tain a  sufficient  percentage  of  the  gold  and  silver,  the  solution  is  drawn 
ofi"  and  the  tailings  are  washed  with  fresh  water;  enough  wash-water 
is  used  to  replace  the  amount  of  the  solution  taken  up  by  the  tailings. 
The  amount  of  water  thus  added  to  the  solution  is  usually  about  500 
gallons  to  six  tons  of  ore.  If  on  testing  the  solution  it  is  not  found  to 
have  dissolved  a  sufficient  percentage  of  the  gold  and  silver,  the  stock 
solution  is  left  on  the  ore  until  all  the  gold  and  silver  which  it  is  pos- 
sible to  extract  by  this  process  has  passed  into  solution.  The  tempera- 
ture of  the  solution  employed  has  varied  from  40°  to  80°  Fahr.,  and 
within  these  limits  no  difference  was  experienced  in  the  solubility  of 
the  gold  and  silver.  In  this  process  it  was  found  to  be  far  better  to 
assay  the  filtered  solution  than  the  macerated  pulp,  for  a  perfect  volu- 
metric sample  of  the  filtrate  can  be  readily  obtained.  Test  assays — 
four  assay-tons  of  the  auriferous  solution  of  cyanide  of  potassium  are 
evaporated,  and  the  resultant  auriferous  compound  is  mixed  with  half 
an  assay-ton  of  litharge,  and  fluxed  with  glass.  The  assay  is  conducted 
as  an  ordinary  assay  for  gold  and  silver." 

"  In  speaking  of  the  different  ores  they  have  treated  by  the  cyanide 
process,  Messrs.  Stebbins  and  Porter  state  that  it  has  been  their  expe- 
rience that  the  majority  of  ores  showing  free  gold  also  contain  gold  in 
any  sulphide  which  may  be  present;  but  that,  except  in  the  case  of 
sulph-arsenides,  ores  showing  no  free  gold  seldom  contain  auriferous 
sulphides.  In  September,  1893,  Messrs.  Stebbins  and  Porter  were  building 
a  mill  in  which  to  treat  ore  by  the  cyanide  process  at  the  Iconoclast  Mine." 

A  cyanide  agitation  plant  was  erected  by  me  (the  author)  in  1893,  at 
the  Utica  Mine,  Calaveras  County,  which,  being  successful  in  all  details, 
shall  here  be  described  in  full.  The  Utica  Mining  Company  are  the 
owners  of  an  extensive  milling  plant,  consisting  of  160  stamps  with  Frue 
vanners  and  Tulloch  concentrators,  and  a  canvas  plant  for  tlie  saving 


90  THE    CYANIDE    PROCESS. 

of  the  sulphuret  slimes  which  escape  from  the  concentrators.  Up  to  last 
year  all  concentrates  were  extracted  by  the  Piattner  chlorination  process, 
wliich  treats  the  coarse  vanner-py rites  well;  the  fine  slimes  of  the  canvas 
plant,  however,  do  not  give  equally  satisfactory  results,  on  account  of 
their  containing  a  very  large  percentage  of  carbonate  of  lime,  which  is 
troublesome  and  involves  loss  in  the  roasting  furnace  on  account  of  its 
fineness  and  lightness,  and  is  costly  in  chlorination  on  account  of  its 
taking  up  chlorine.  The  slimes  are  also  difficult  to  leach  in  the  chlori- 
nation vats.  I  examined  the  different  classes  of  concentrates  as  to  their 
fitness  for  treatment  with  cyanide.  The  coarser  sulphurets  from  the 
concentrators  did  not  give,  without  further  grinding,  sufficiently  high 
extraction  results  to  warrant  the  substitution  of  the  chlorination  by  the 
cyanide  process.  The  results  of  the  experiments  with  the  slimes  from 
tiie  canvas  plant,  which  were  very  satisfactory,  led  to  the  construction 
of  the  present  agitation  plant.  This  plant  (see  illustration)  is  com- 
pletely built  of  steel  and  iron,  and  consists  of  the  following  parts:  A 
vertical  cylindrical  agitator  (constructed  by  Mr.  C.  D.  Lane  and  myself), 
5  ft.  in  diameter  by  5  ft.  high,  of  ^in.  steel  plate,  with  a  cast-iron  bottom 
2  in.  thick,  with  strengthening  ribs  underneath;  to  the  bottom  is  cast  a 
cone,  through  w^hich  passes  the  vertical  shaft,  which  carries  four  arms. 
To  these  are  attached  the  four  paddles  of  ^  in.  steel,  6  in.  wide,  twisted 
like  the  plates  of  a  propeller.  A  ring  connecting  the  four  paddle  arms 
gives  greater  stability  to  them.  The  shaft  with  the  paddles  can  be 
raised,  by  means  of  a  screw-spindle,  4  ft.  above  the  bottom  of  the  appa- 
ratus. A  wrought-iron  ring,  3  in.  wide  and  ^  in.  thick,  riveted  outside 
around  the  top  of  the  agitator,  strengthens  the  structure.  The  driving 
gear  is  placed  below.  An  opening,  4  in.  diameter,  in  the  bottom,  dis- 
charges the  contents  of  the  agitator  through  a  pipe,  furnished  with  a 
stopcock,  onto  Scheidel's  patent  vacuum  filter,  placed  on  the  floor 
below  and  in  front  of  it.  Here  a  perfect  separation  of  the  cyanide 
gold  solution  is  effected  from  the  residues.  This  filter  (see  diagram) 
is  built  of  i  in.  steel,  with  bottom  ■§  in.  thick;  it  forms  a  rectangular 
box  3  ft.  6  in.  deep,  7  ft.  long  by  5  ft.  wide;  2  ft.  above  the  bottom  is  a 
perforated  steel  filter-bottom  of  |  in.  boiler  plate,  made  in  three  mov- 
able sections,  supported  by  angle-iron  running  around  the  sides,  and 
by  the  vertical  support  of  double  T  iron.  The  perforations  are  of  ^  in. 
diameter,  at  a  distance  of  ^  in.  from  each  other.  This  filter-bottom  fits 
closely  to  the  sides  of  the  apparatus;  it  is  covered  with  a  blanket,  which 
is  kept  in  position  by  bars  running  along  the  four  sides,  and  fastened 
by  thumb  screws.  A  grating  in  three  sections  of  f  in.  round  iron  serves 
to  protect  the  cloth;  the  intervals  of  3  in.  between  the  bars  are  filled 
in  with  coarse  sand.  The  filter  partition  divides  the  apparatus  into 
two  compartments,  one  above  the  other;  the  lower  forms  a  closed  box, 
which  is  in  connection  with  a  duplex  vacuum  pump,  by  means  of  which 
the  air  can  be  rarefied  when  the  filter-bottom  is  covered  with  pulp. 
The  upper  part,  above  the  filter-bottom,  receives  the  contents  of  the  agi- 
tator. The  real  bottom  of  the  apparatus  has  a  discharge  with  a  3  in. 
stopcock,  for  running  off  the  filtered  solution  into  either  one  or  the 
other  of  the  two  solution  tanks,  which  are  standing  on  the  floor  one  step 
lower,  in  front  of  the  filter.  All  cocks  and  taps  of  the  plant  are  of  con- 
siderable diameter,  which  secures  a  quick  charge  and  discharge.  The 
filter  is  provided  with  a  gauge  to  indicate  the  height  of  the  solution 
within,  a  gauge  indicating  the  degree  of  vacuum,  an  air-tap  to  permit 
influx  of  air  when  the  filtered  solution  is  being  discharged,  and  a  manhole. 


^ 
^ 
^ 


T«HjCmku*v>tN**'>'>. 


EXEMPLIFICATION    OF   PROCESS THE    PROCESS    IN   CALIFORNIA.  91 

The  mode  of  working  the  plant  is  this:  The  cyanide  solution  is 
charged  into  the  agitator,  the  paddles  are  set  in  motion  by  revolving  the 
shaft,  the  ore  is  charged  b}'-  degrees,  and  the  agitation  is  kept  up  for  the 
required  time,  after  which  the  pulp  is  discharged  from  the  agitator  onto 
the  filter.  The  vacuum  pump  is  then  set  in  motion,  and  filtration  under 
the  influence  of  atmospheric  pressure  will  at  once  commence.  The  solu- 
tion will  soon  be  sucked  through;  then  washing  follows,  first  with  liquor 
from  former  operations,  which  has  already  passed  through  the  zinc 
boxes,  and  finally  with  clear  water.  These  operations  of  filtering  and 
washing  take  about  two  hours.  It  is  advisable  to  suck  the  tailings  as 
dry  as  possible  before  each  new  wash  is  put  on,  which  permits  the  com- 
plete removal  of  the  gold  solution  with  a  very  small  amount  of  liquid, 
one  half  ton  of  which  is  sufficient  for  washing  a  charge  of  two  tons  of  ore. 
If  the  filtration  has  been  properly  managed,  no  degree  of  continued 
washing  can  improve  the  results.  The  -filtered  solutions  are  clear.  The 
first  or  original  solution,  together  with  the  first  wash,  will  be  run  oft'  into 
one  of  the  two  solution  tanks  in  front  below  the  vacuum  filter;  the  follow- 
ing washes  run  into  the  other.  These  tanks  are  8  ft.  long  by  3  ft.  wide 
and  3  ft.  deep,  made  of  i  in.  steel.  Each  of  the  tanks  is  in  connection 
with  a  zinc  precipitation  box,  9  ft.  long  by  21  in.  deep  and  9  in.  wide, 
divided  into  ten  compartments;  there  is  an  interval  of  1  in.  between 
each  two  compartments.  The  false  perforated  steel  bottoms  of  the 
chambers,  which  can  be  removed  if  desired,  are  2^  in.  above  the  true 
bottom  of  the  box  (see  diagram,  p.  31).  The  bottom  of  the  box  has  a 
number  of  1  in.  iron  faucets,  one  corresponding  with  the  center  of  each 
filter  compartment;  the  sides  of  the  box  are  4  in.  higher  than  the  par- 
titions within,  which  insures  absolute  safety  against  the  liquid  running 
over  the  sides  of  the  box,  if  one  or  the  other  compartments  should  become 
blocked.  The  gold  solution  flows  into  the  box  through  a  1  in.  cock,  enters 
the  first  compartment  from  below  through  the  perforated  false  bottom, 
percolates  the  zinc  shavings  placed  thereupon,  leaves  it,  and  enters  the 
second,  and  so  forth.  A  steel  settling  tank.  12  in.  deep,  12  in.  wide,  and 
9  ft.  3  in.  long,  is  placed  below  the  precipitating  box  for  receiving  the 
bullion  when  cleaning  up  (see  general  demonstration  of  process,  above). 
The  zinc  used  consists  in  turnings  of  ^o  o'  i^^-  thick,  turned  from  cast 
zinc  cylinders  on  a  lathe;  2  lbs.  fill  one  compartment.  The  solution 
passes  through  the  box  at  the  rate  of  700  gallons  in  twenty-four  hours. 
The  bullion  precipitation  of  the  solution  is  very  efficient  as  it  passes 
from  compartment  to  compartment,  which  amounts  to  passing  ten  times 
through  a  zinc  column  of  14  in.  high  by  9  in.  square.  As  shown  by  the 
following  table  of  analysis. 


One  Ton  of  Liquid  contains— 

Gold 

Silver. 

Originallv 

Oz.    Dwts. 

5        14 

16 

5 

2 

1 

1 

Grs. 
0 

I 

14 

4 

1 
22 

15.43 
14.96 
13..36 
12.34 

Oz.     Dwts. 
2          4 
5 
1 

Grs. 
g 

After  14  in.  of  zinc  column 

After  28  in.  of  zinc  column 

3 
10 

After  42  in.  of  zinc  column  . . 

17 

After  56  in.  of  zinc  column  .-. 

12 

After  70  in.  of  zinc  column 

11 

After  84  in.  of  zinc  column 

3 

After  98  in.  of  zinc  column 

0 

After  112  in.  of  zinc  column . 

0 
0 

After  126  in.  of  zinc  column 

After  140  in.  of  zinc  column 

0 

92 


THE    CYANIDE    PROCESS. 


11X5 


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The  solution  leaving  the  zinc  box  contains  only  12.34  grs.  of  gold, 
or  0.0045  per  cent  of  its  original  contents,  and  only  3  grs.  of  silver,  or 
0.0028  per  cent  of  the  original  silver  value.  Simultaneously  the  solu- 
tions were  analyzed  for  available  cyanide,  but  no  decrease  in  the  strength 
of  the  solution,  which  remained  constantly  at  0.3185  per  cent,  could  be 
ascertained.      "At  another  period  I  studied  the  solubility  of   zinc  in 


BXEMPLIFICATlON   OF    PROCESS — THE    PROCESS   IN    CALIFORNIA.  93 

cyanide  solution,  of  which  I  give  the  following  figures:  0.2634  grs.  of 
filiform  zinc  were  submerged  in  50  cc.  cyanide  solution  of  0.26  per 
cent;  after  seven  days  of  frequent  agitation  these  were  reduced  to  0.2584 
grs.,  and  after  fifty-six  days  to  0.2252  grs.,  which  means  that  after  seven 
days  1.98  per  cent,  and  after  fifty-six  days  14.47  per  cent  of  the  zinc 
were  dissolved.  From  this  observation  it  follows  that  the  loss  of  cyanide 
in  the  precipitating  boxes,  by  means  of  its  being  taken  up  by  zinc,  is 
sometimes  overestimated."  The  washes  pass  through  a  similar  precipi- 
tating box.  The  liquids,  when  leaving  these  boxes,  go  as  liquor  No.  1 
and  liquor  No.  2,  into  tanks  of  the  same  size  as  the  solution  tanks,  from 
where  a  pump  will  deliver  them  wherever  wanted.  Liquor  No.  1  serves 
for  making  up  the  new  solution  for  the  next  charge;  liquor  No.  2  is  used 
for  washing  purposes  on  the  vacuum  filter.  No  liquor  ever  leaves  the 
works;  the  quantity  in  circulation  remains  stationary.  The  bullion 
obtained  from  the  zinc  boxes  is  passed,  as  formerly  described,  through 
a  sieve  onto  the  bullion  vacuum,  which  itself  is  a  miniature  reproduc- 
tion of  the  vacuum  filter  (see  diagram).  It  has  the  following  dimen- 
sions: Length,  2^  ft.;  width,  2  ft.;  total  depth,  1  ft.  6  in.  The  per- 
forated filter-bottom  is  fixed  12  in.  above  the  true  bottom.  The  bullion 
is  very  slimy;  in  fact,  it  is  the  more  slimy  the  freer  it  is  from  zinc;  its 
filtration  and  washing  take  some  time.  When  the  mass  is  tolerably 
dry,  it  is  put  into  a  wooden  tub  and  treated  with  diluted  sulphuric  acid. 
The  heat  of  the  reaction  I  have  always  found  sufiicient  to  make  the 
operation  a  speedy  and  satisfactory  one;  the  bullion  is  then  permitted 
to  settle,  the  liquid  is  siphoned  off  through  the  bullion  filter,  and  the 
solid  matter  is  washed  by  decantation  with  water.  This  washing  process 
is  continued  until  all  soluble  salts  are  removed.  The  bullion  is  then  par- 
tially dried  on  the  filter,  and  finally  dried  in  a  small  muffle  furnace; 
complete  drying  of  the  bullion  by  artificial  heat  before  the  acid  treatment 
is  not  advisable.  The  thoroughly  dry  bullion  is  pulverized  and  well 
mixed  with  soda  and  borax,  and  melted  in  a  plumbago  crucible  as 
described  before.  The  bullion  thus  obtained  is  946  fine;  the  slag  is 
clean,  it  contains  the  usual  few  granules  of  bullion,  but,  freed  from  them, 
does  not  give  any  assay  results.  The  bullion  could  be  still  further 
refined,  but  to  no  commercial  advantage.  The  steel  of  the  tanks  has 
not  as  yet  shown  any  effects  from  cyanide,  nor  does  it  exercise  any 
influence  on  the  solutions.  All  apparatus  is  composed  of  plates  and 
sheets  riveted  together;  leakages,  if  any,  can  be  easily  stopped  by  a 
varnish  made  of  asphaltum  dissolved  in  bi-sulphide  of  carbon.  As 
mentioned,  this  plant  has  been  constructed  for  the  treatment  of  slime 
concentrates  from  the  canvas  plant;  such  concentrates  contain  a  vary- 
ing percentage  of  carbonate  of  lime,  in  some  instances  as  much  as  95 
per  cent,  which,  however,  does  not  interfere  mechanically  or  otherwise 
with  their  satisfactory  extraction  by  cyanide.  Such  conditions  would 
make  chlorination  all  but  impossible,  as  alluded  to  before.  For  agita- 
tion the  material  requires  an  amount  of  solution  equal  to  30  per  cent  of 
its  weight,  and  six  hours  of  time.  The  described  plant  is  capable  of  treat- 
ing a  much  larger  amount  of  slimes  than  are  usually  produced  per  day 
by  the  canvas  plant;  its  services  are  therefore  only  periodically  required. 
The  average  consumption  of  cyanide,  calculated  from  a  large  tonnage  of 
slimes  treated,  amounted  to  4.3  lbs.  per  ton,  costing  $2  27;  the  labor 
amounts  to  $1;  the  total  expenses  of  treatment  by  cyanide  to  $3  50  per 
ton.     The  average  extraction  amounts  to  93.18  per  cent  of  the  gold,  and 


94 


THE    CYANIDE    PROCESS. 


90  per  cent  of  the  silver  assay-value;  as  high  as  96.57  per  cent  of  the 
gold  has  been  extracted  in  some  instances.  The  extraction  of  the  gold 
during  the  agitation  goes  on  as  shown  by  this  table: 


Treatment  of  Slimes  by  Agitation. 


Gold  per 
Ton. 


Extraction— 
Per  Cent. 


Sample  before  treatment 

Sample  after  1  hour's  agitation 
Sample  after  2  hours'  agitation 
Sample  after  3  hours'  agitation 
Sample  after  4  hours'  agitation 
Sample  after  5  hours'  agitation 
Sample  after  6  hours'  agitation 
Sample  after  7  hours'  agitation 
Sample  after  8  hours'  agitation 


$88  00 

13  00 

11  00 

7  00 

7  00 

6  00 

5  00 

5  00 

5  00 

85.23 
87.50 
92.05 
92.05 
93.18 
94.31 
94.31 
94.31 


Within  the  first  hour  85.23  per  cent  of  the  gold  are  extracted;  during 
the  following  five  hours  the  increase  of  extraction  is  slow  and  irregular; 
after  six  hours  no  further  extraction  takes  place.  For  experimental  pur- 
poses I  continued  agitation  up  to  twelve  hours  without  improving  on  the 
result.  The  treatment  of  the  slime  concentrates  by  agitation  was  pre- 
ferred on  account  of  its  quicker,  cheaper,  and  better  results,  as  compared 
with  percolation.  All  Utica  concentrates,  as  in  fact  all  concentrates  I 
ever  had  to  deal  with,  contain  a  small  amount  of  amalgam,  part  of 
which  is  found  on  the  bottom  of  the  agitator;  part  of  it  leaves  the  works 
with  the  tailings,  and  is  recovered  in  Hungarian  riffles  and  on  amal- 
gamated silver  plates;  part  of  the  mercury  goes  undoubtedly  into  the 
cyanide  solution,  and  is  precipitated  with  the  bullion  in  the  zinc  boxes. 

Other  sulphurets,  such  as  the  Frue  vanner  concentrates  of  the  Utica, 
Madison,  and  Eureka  mines,  were  treated  on  a  more  or  less  extensive 
scale  by  the  same  plant;  results  were,  however,  not  very  satisfactory  on 
account  of  their  coarseness.  All  sulphurets  of  the  Utica  Mine  are  pure 
sulphide  of  iron.  The  fine  canvas-plant  concentrates,  although  less 
clean,  are  as  a  rule  richer  in  gold;  their  extraction  averaged  93.18  per 
cent,  whereas  the  vanner  concentrates  gave  only  81.38  per  cent,  which, 
although  reasonably  good  at  the  rate  of  -$4  per  ton  cost  of  treatment, 
cannot  compete  with  a  chlorination  treatment,  which  yields  90  per  cent 
of  a  $50  ore  at  a  cost  of  $6  50.  (The  large  size  of  the  Utica  chlorination 
works  oflers  special  advantages  and  permits  chlorination  at  this  figure, 
which  is  much  lower  than  the  cost  anywhere  else  in  California.)  A  large 
number  of  tests  proved  that  a  high  percentage  of  the  gold  is  contained  in 
the  coarser  particles  of  the  sulphurets;  this  will  account  to  some  extent 
for  the  comparatively  low  percentage  of  cyanide  extraction.  It  would 
lead  too  far  to  give  here  the  results  of  the  large  number  of  experiments 
in  reference.  The  experiments  were  extended  to  roasted  concentrates 
after  their  reduction  to  uniform  size,  which  gave  on  a  small  scale  excellent 
results  (98.09  per  cent  extraction).  I  am  indebted  to  Colonel  Hay- 
ward,  Mr.  Charles  D.  Lane,  and  Mr.  James  Cross,  of  the  Utica  Mine, 
for  their  permission  to  publish  the  diagrams  and  the  described  results 
of  the  cyanide  works  which  I  erected  for  them.  The  cost  of  the  plant 
is  divided  as  follows: 

Grading  and  foundations - - $200  00 

Biiilding 300  00 

Shafting,  belting,  and  puttmg  into  place 135  00 

Agitator 260  00 

Vacuum  filter --- - -- 165  00 


EXEMPLIFICATION    OF    PROCESS — THE    PROCESS    IN    MEXICO,    ETC.  95 

Three  tanks - $160  00 

Two  zinc  boxes 260  0<J 

Two  steel  tanks ^5  00 

One  vacuum  pump 235  00 

One  liquid  pump 130  00 

Pipes,  stopcocks,  faucets,  etc. 70  00 

Total $2,000  00 

The  Standard  Consolidated  Mining  Company,  Bodie,  California,  started 
a  100-ton  cyanide  plant  (50-ton  vats)  on  September  17th  for  the  treat- 
ment of  tailings. 

The  amount  of  ores,  fine  concentrates,  and  tailings  suitable  for 
cyanide  treatment  is  considerable  in  this  State.  There  is  no  doubt  that 
a  great  amount  of  gold  is  now  being  lost  with  the  slimes  in  most  mills 
here,  as  elsewhere,  and  in  many  instances  dry-crushing  of  the  ore  and 
direct  cyanide  treatment  would  vastly  increase  the  returns.  Coarse 
gold,  if  present,  can  be  saved  by  amalgamation  at  some  later  stage  of 
the  manipulation. 

Generally  speaking,  the  number  of  commercial  successes  of  the  process 
in  the  United  States  is  limited,  although  the  number  of  tests  and  trials 
on  a  smaller  or  larger  scale  have  been  very  numerous.  The  amount  of 
ores  suitable  for  the  treatment  is  large,  and  the  process  is  becoming 
more  and  more  an  established  and  acknowledged  fact  with  the  mining 
public.  The  miners  of  this  country  have  long  been  looking  for  a  process 
for  the  treatment  of  low-grade  sulphurets  which  is  cheaper  in  its  appli- 
cation than  chlorination.  Under  certain  conditions  the  cyanide  process 
meets  the  requirements,  and  will  be  found  particularly  valuable  in 
remote  places  to  which  the  freight  expenses  are  high.  The  weight  of 
chemicals  used  in  chlorination  amounts  to  about  5  per  cent  of  the  ore 
weight,  but  only  to  about  1  per  cent  in  the  case  of  cyanide  treatment. 
By  chlorination  one  ton  of  chemicals  will  treat  about  twenty  tons  of 
ore,  whereas  by  cyanide  one  ton  will  treat  100  tons;  moreover,  the 
cyanide  process  does  not  require  a  special  treatment  of  the  ore  for  the 
extraction  of  the  silver.  No  statistics  in  reference  to  the  gold  produced 
in  the  United  States  of  America  by  the  cyanide  process  could  be  obtained 
by  the  author. 

D.    Mexico,  Etc. 

A  MacArthur-Forrest  company  is  introducing  the  process  in  that  old 
mining  country.  No  information,  however,  could  be  obtained  from 
that  company  in  reference  to  their  results.  In  other  parts  of  the 
world,  attempts  have  been  made,  chiefly  by  the  owners  of  the  Mac- 
Arthur-Forrest  patents,  to  introduce  the  cyanide  process.  Ores  from 
the  republic  of  Colombia  are  reported  as  having  been  treated  with 
success,  and  the  introduction  of  the  process  into  that  country  is  now 
intended.  Negotiations  for  the  introduction  of  the  process  into  the 
Straits  Settlements,  Borneo,  the  mining  States  of  South  America,  and 
that  great  gold-producing  country,  Russia,  are  now  pending. 

I  have  in  this  paper  been  following  the  cyanide  process  in  its  workings 
and  results  through  the  chief  places  of  its  application.  The  process,  like 
most  metallurgical  processes,  has  its  weak  points,  which  by  continued 
investigations  may  be  strengthened;  its  strong  points  are  evident  from 
the  description  of  its  successful  application.  Whatever  may  be  the  merit 
of  the  controversy  on  the  subject  of  patent-rights  in  connection  with  this 


96  THE    CYANIDE    PROCESS. 

process,  there  is  no  doubt  that  Messrs.  MacArthur  and  Forrest  deserve 
the  credit  of  having  first,  on  a  large  scale,  practically  and  successfully 
applied  the  cyanide  process  for  working  ores. 


SUMMARY  AND  CONCLUSIONS. 

Generally  speaking,  the  cyanide  process  is  better  suited  for  the  treat- 
ment of  gold  ores  than  of  silver  ores,  one  of  the  reasons  of  which  may  be 
found  in  the  great  variety  of  compounds  in  which  the  silver  occurs,  and 
a  number  of  these  offer  difiiculties  in  treatment.  The  required  long 
contact  of  cyanide,  connected  with  the  large  consumption  of  reagent, 
prevents  the  treatment  of  silver  ores  in  some  instances  from  being  a 
commercial  success,  even  when  chemically  a  high  extraction  is  obtained. 
In  reference  to  the  general  characteristics  of  ores  which  can  be  success- 
fully treated,  it  must  be  said  that  no  definite  specification  can  be  given. 
The  question,  Is  an  ore  suited  for  cyanide  treatment?  can  only  be  decided 
experimentally.  Preliminary  but  exhaustive  experiments  on  a  limited 
scale  should  precede  all  operations  on  a  large  scale.  Many  of  the  prob- 
lems of  the  process  are  of  a  chemical  nature;  many  of  its  difficulties  are, 
however,  of  a  mechanical  character,  and  experience  and  judgment  must 
guide  in  the  selection  of  the  plant  to  make  the  venture  a  financial  suc- 
cess. One  of  the  great  mechanical  difficulties  has  been,  and  is  still,  the 
treatment  of  the  slimes,  by  which  is  meant  the  very  finest  parts  and  the 
clayey  portion  of  ores  and  tailings.  The  final  solution  of  the  difficulty 
in  their  treatment  will  probably  be  found  in  dry-crushing  the  ore  and 
direct  treatment  of  the  crushed  material  with  cyanide.  In  cases  where 
coarse  gold  is  present,  the  amalgamation  of  such  may  be  introduced  at 
some  later  periods  of  the  manipulation.  Practical  experience  with  the 
process  extends  over  only  a  few  years.  It  has  been  found  to  be  well 
adapted  for  free-milling  ores  with  finely  divided  gold,  particularly 
so-called  float  gold,  and  has  given  great  satisfaction  with  some  pyritic 
ores.  Even  complex  ores  containing  tellurides  have  been  treated  to 
advantage.  The  process  has  fourtd  its  most  extensive  application  on 
the  Transvaal  gold  fields;  although  the  average  extraction  is  not 
high,  it  answers  there  better  than  any  other  process  attempted  for 
working  the  tailings.  In  other  parts  of  the  gold-producing  world,  its 
application  is  gaining  way  by  degrees.  Like  all  metallurgical  pro- 
cesses, its  success  depends  on  the  character  of  the  ore  and  local  cir- 
cumstances, and  failures  had  to  be  recorded  where  these  were  not 
sufiiciently  considered.  It  is  certain  that  our  knowledge  is  as  yet 
incomplete,  and  there  is  still  a  large  amount  of  ground  for  the  metallur- 
gist and  chemist  to  explore.  We  have  yet  particularly  to  learn  how 
to  extend  the  application  of  the  process  to  more  common  use.  A  com- 
parison of  the  cyanide  process  with  other  processes  is  a  futile  task;  the 
great  merit  of  the  treatment  is  that  it  comes  to  fill  a  want  long  felt — that 
of  treating  low-grade  ores  and  tailings  in  a  simple  and  inexpensive  way. 
It  is  here  that  the  process  antagonizes  no  other  methods,  and  simply 
takes  its  place  in  gold  metallurgy  as  a  new  and  powerful  means  to  con- 
quer nature.  Wherever  the  process  gives  satisfactory  results,  it  offers 
great  advantages:  it  does  not  require  roasting  furnaces;  ores  containing 
lead,  zinc,  or  earthy  carbonates,  which  cannot  be  worked  to  a  profit  by 
chlorination,  may  be  easily  and  profitably  treated  by  it;  as  it  does  not 


SUMMARY   AND   CONCLUSIONS.  97 

require  smelters,  coal,  and  fluxes,  it  may  be  successfully  used  in  remote 
situations,  where  smelting  is  absolutely  impossible.  One  of  its  great 
advantages  is,  it  does  not  require  extra  treatment  for  silver,  invariably 
associated  with  gold  in  ore.  I  have  generally  spoken  about  gold  only 
in  this  paper.  The  remarks  referring  to  it  and  to  its  extraction  apply 
with  equal  force  to  the  silver  associated  with  it.  A  well-constructed 
plant  and  efficient  chemical  and  metallurgical  supervision  are,  however, 
conditions  always  necessary  to  make  its  application  a  commercial  suc- 
cess. The  process  is  only  in  its  infancy;  many  of  the  various  and 
complex  problems  it  has  given  rise  to — such  as  the  reduction  in  the 
consumption  of  cyanide  and  its  regeneration — are  still  open  questions. 
Its  possibilities  are  great;  chemical  and  mechanical  improvements  will 
enlarge  the  range  of  its  application  and  usefulness.  If  it  has  not  proved 
itself  to  be  the  metallurgical  panacea  that  some  enthusiasts  expected, 
it  has  certainly  during  the  four  years  of  its  technical  application  devel- 
oped into  a  process  of  enormous  economical  importance,  and  one  which 
justly  may  be  considered  a  most  valuable  addition  to  gold  metallurgy. 


7cp 


APPENDIX. 


APPENDIX. 


UNITED  STATES  PATENT  OFFICE. 


JULIO  H.  REA,  OF  Syracuse,  New  York. 
IMPROVED  MODE  OF  TREATING  AURIFEROUS  AND  ARGENTIFEROUS  ORES, 


Specification  forming  part  of  Letters  Patent  No.  61,866,  dated  February  5,  1867. 

To  all  whom  it  may  concern: 

Be  it  known  that  I,  Julio  H.  Rae,  of  Syracuse,  in  the  county  of  Onondaga  and  State  of 
New  York,  have  invented  a  new  and  useful  Improvement  in  Treating  Auriferous  and 
Argentiferous  Ores;  and  I  do  hereby  declare  that  the  following  is  a  full,  clear,  and  exact 
description  thereof,  which  will  enable  those  skilled  in  the  art  to  make  and  use  the  same, 
reference  being  had  to  the  accompanying  drawing,  forming  part  of  this  specification,  in 
which — 

Figure  1  represents  a  transverse  vertical  central  section  of  thfi  apparatus  which  may  be 
used  in  carrying  out  this  invention. 

Figure  2  is  a  plan  or  top  view  of  the  same. 

Similar  letters  of  reference  in  both  views  indicate  corresponding  parts. 

This  invention  consists  in  treating  auriferous  and  argentiferous  ores  with  a  current  of 
electricity  or  galvanism  for  the  purpose  of  separating  the  precious  metals  from  the 
gangue.  In  connection  with  the  electric  current  suitable  liquids  or  chemical  prepara- 
tions, such,  for  instance,  as  cyanide  of  potassium,  are  used,  in  such  a  manner  that  by  the 
combined  action  of  the  electricity  and  of  the  chemicals,  the  metal  contained  in  the  ore 
is  first  reduced  to  a  state  of  solution  and  afterwards  collected  and  deposited  in  a  pure 
state,  and  that  the  precious  metals  can  be  extracted  from  the  disintegrated  rock  or  ore 
at  a  very  small  expense  and  with  little  trouble  or  loss  of  time. 

In  carrying  out  this  process  a  jar.  A,  may  be  used  such  as  shown  in  the  drawing. 
This  jar  is  made  of  glass  or  other  suitable  material  (the  size  depending  upon  the  elec- 
tric battery  to  be  used  in  connection  therewith),  and  into  said  jar  is  placed  the  pulver- 
ized rock,  filling  the  same  half  full  or  more.  On  the  rock  is  poured  the  proper  chemical 
preparation  in  a  fluid  state,  such,  for  instance,  as  cyanide  of  potassium.  Tlirough  the  cen- 
ter of  the  jar  passes  a  vertical  shaft  C,  whicn  terminates  upon  a  metal  plate,  a,  by  pref- 
erence of  platma,  which  rests  on  the  bottom  of  the  jar,  and  to  said  shaft  is  attached  a 
cage,  B,  of  platina  wire  or  other  suitable  material.  This  cage  is  made  in  the  form  of  a 
truncated  cone,  its  base  extending  close  to  the  inner  circumference  of  the  shaft,  or  it  may 
be  made  in  any  other  suitable  form  or  shape,  a  series  of  spirals,  for  instance,  which  will 
produce  the  same  effect.  On  the  shaft  G  is  mounted  a  pulley,  E,  which  may  be  con- 
nected with  any  suitable  mechanism  for  the  purpose  of  imparting  a  rotary  motion  to  said 
shaft  and  the  cage  connected  therewith,  so  that  the  contents  of  the  jar  will  be  agitated 
and  each  particle  of  the  pulverized  rock  shall  come  in  contact  with  the  metal  cage  B 
and  plate  a.  The  shaft  C  is  connected  by  a  wire,  6,  with  one,  say  the  positive  pole  of  the 
battery,  thus  converting  the  shaft,  the  cage,  and  the  plate  a  into  an  electrode,  and  the 
other  or  negative  pole  of  the  battery  connects  by  a  wire,  c,  with  a  thin  slip  or  coil,  d,  of 
copper  or  other  suitable  material,  forming  a  base  on  wliich  the  precious  metals  are 
deposited.  By  the  action  of  the  electric  current  the  action  of  the  chemicals  on  the  met- 
als contained  in  the  rock  is  materially  faciliated  and  a  perfect  solution  thereof  is 
effected,  and  from  this  solution  the  precious  metals  are  precipitated  upon  the  base  d, 
whence  the  same  can  be  easily  collected.  By  this  process  gold  or  silver  can  be  extracted 
from  rock  in  an  absolutely  pure  state  and  with  very  little  expense. 

What  1  claim  as  new,  and  desire  to  secure  by  Letters  Patent,  is — 

1.  The  within-described  process  of  treating  auriferous  or  argentiferous  rock  by  expos- 
ing the  same  to  the  combined  action  of  a  current  of  electricity  and  of  suitable  solvents 
or  chemicals,  substantially  such  as  herein  specified,  or  any  others  which  will  produce 
the  same  effect. 

2.  Separating  gold  or  silver  from  the  rocks  containing  the  same  by  the  action  or  aid 
of  electricity,  substantially  as  described. 

3.  Using  the  agitator  B  as  an  electrode  substantially  as  and  for  the  purpose  set  forth. 

JULIO  H.  RAE, 
Witnesses: 
W.  Haxjff. 
Geo.  F.  Southern. 


102 


THE   CYANIDE   PROCESS. 


J.  H.  RAL 
Treating  Ores. 


No.  61.866. 


Patented  Feb.  5,  1867. 


..^Zf^  -^ 


Jhoy^riti?/* 


PATENT-SPECIFICATIONS.  '  103 

UNITED  STATES  PATENT  OFFICE. 


THOMAS  C.   CLARK,    of   Oakland,    assignor    to    JAMES    STRATTON,  of    samk 
PLACB,  AND  RICHARD  E.  COADY,  of  Alameda,  California,  one  fourth  to  each. 

EXTRACTING  PRECIOUS  METALS  FROM  ORES. 


Specification  forming  part  of  Letters  Patent  No.  229,586,  dated  July  6, 1880. 
(Application  filed  December  27, 1879.) 

To  all  whom  it  may  concern : 

Be  it  known  that  I,  Thomas  C.  Clark,  of  Oakland,  county  of  Alameda,  and  State  of 
California,  have  invented  an  Improvement  in  Extracting  Precious  Metals  from  ores ; 
and  I  hereby  declare  the  following  to  be  a  full,  clear,  and  exact  description  thereof. 

The  object  of  my  invention  is  to  perform  the  disintegration  and  desulphurization  of 
ores  so  as  to  bring  the  said  ore  into  proper  condition  for  easy  pulverization  and  the 
precious  metals  contained  therein  into  a  suitable  form  for  amalgamation  by  freeing 
them  from  the  union  and  influence  of  baser  metals.  In  order  to  accomplish  this  object 
the  ore  is  crushed  into  pieces  about  the  size  of  ordinary  Indian  corn.  That  portion 
containing  sulphurets  generally  becomes  finer,  since  it  is  more  friable.  The  object  of 
crushing  it  to  this  size  is  to  prevent  loss  of  gold  and  to  facilitate  washing  operations. 

The  ore,  after  being  crushed  as  described,  is  placed  in  an  ordinary  roasting-furnace. 
After  being  roasted  for  a  suitable  length  of  time  the  heat  is  raised,  so  the  sulphur  will 
burn  freely,  after  which  the  heat  is  let  down  again,  a  free  supply  of  oxygen  being  fur- 
nished during  the  whole  process  of  roasting. 

After  the  ore  has  become  dead  and  lies  like  sand  in  the  furnace,  and  no  more  scintilla- 
tion is  apparent,  it  is  heated  up  to  a  good  red  heat,  but  not  made  too  hot. 

In  a  suitable  receptacle  beside  the  furnace  I  form  a  cold  bath,  into  which  the  ore  is 
drawn  while  in  its  heated  condition  fresh  from  the  furnace.  This  bath  is  formed  of  a 
solution  of  salt,  prussiate  of  potash,  and  caustic  soda  or  caustic  potash. 

For  one  ton  of  gold  ore  containing  five  per  cent  or  less  of  sulphurets,  I  form  my  bath 
in  about  the  following  proportions:  I  take  about  thirty  gallons  of  cold  water,  to  which 
common  salt  is  added  until  a  saturated  solution  is  formed.  I  then  dissolve  one  pound  of 
prussiate  of  potash  in  water  and  pour  it  into  the  solution,  and  also  dissolve  one  pound 
of  caustic  soda  in  water  and  add  it  to  the  solution.  The  bath  then  contains  chloride  of 
sodium,  prussiate  of  potash,  and  caustic  soda.  For  the  latter  caustic  potash  may  be 
substituted  with  a  like  result. 

The  red-hot  ore  being  drawn  into  the  cold  solution  described,  a  complete  desulphur- 
ization is  effected,  as  well  as  a  disintegration. 

Where  there  is  a  higher  percentage  of  sulphur  in  the  ore,  additional  quantities  of  the 
prussiate  of  potash  and  caustic  soda  are  added,  the  proportions  of  the  solution  being 
thus  altered  to  suit  the  requirements  of  the  class  of  ore  under  treatment.  The  propor- 
tions may  also  be  modified  for  ore  of  different  character. 

I  am  aware  that  ore  has  frequently  been  roasted  and  dumped  while  red  hot  into  cold 
water  or  into  cold  solutions,  and  I  therefore  do  not  claim,  broadly,  such  process ;  but 

What  I  do  claim  as  new,  and  desire  to  secure  by  Letters  Patent,  is — 

The  process  of  disintegrating  and  desulphurizing  ores  and  freeing  the  precious  metals 
therein  contained,  consisting  m  first  roasting  the  ore  to  a  red  heat,  and  while  in  that 
condition  placing  it  in  a  cold  bath  composed  of  a  solution  of  salt,  prussiate  of  potash, 
and  caustic  soda  or  caustic  potash,  in  about  the  proportions  named,  substantially  as 
herein  described. 

In  witness  whereof  I  have  hereunto  set  my  hand. 

THOMAS  C.  CLARK. 

Witnesses : 

Chas.  G.  Yalb.  I 

S.  H.  NotTBSE. 


104  THE   CYANIDE    PROCESS. 

UNITED  STATES  PATENT  OFFICE. 


HIRAM  W.  FAUCETT,  of  St.  Louis,  Missoubi. 
PROCESS  OF  TREATING  ORE. 


Specification  forming  part  of  Letters  Patent  No.  236,424,  dated  Janiiary  11,  1881. 

(Application  filed  July  13, 1880.    No  specimens.) 

To  all  whom  it  may  concern: 

Be  it  known  that  I,  Hiram  W.  Faucett,  a  citizen  of  the  United  States,  residing  at  St. 
Louis,  in  the  county  of  St.  Louis  and  State  of  Missouri,  have  invented  new  and  useful 
Improvements  in  Process  of  Treating  Ores,  of  which  the  following  is  a  specification. 

The  object  of  my  invention  is  to  treat  all  refractory  ores  containing  gold  and  silver 
for  the  purpose  of  separating  such  metals  from  the  ore. 

It  is  well  known  that  the  chemical  nature  of  all  refractory  ores  is  more  or  less  of  a 
silicious  character,  and  by  desulphurizing  or  roasting  such  ores  they  are  rendered  porous. 
Taking  advantage  of  this  fact,  I  subject  the  silicious  ore  to  a  proper  chemical  bath 
under  pressure,  which  effectually  disintegrates  the  ore  by  decomposing  or  destroying 
the  silica  therein,  which  silica  is  the  chemical  agent  in  the  ore  which  holds  or  locks  the 
ore  together  in  a  compact  mass. 

To  this  end  my  invention  consists,  broadly,  in  subjecting  hot  crushed  ores  to  the 
action  of  disintegrating  chemicals  in  solution  while  under  pressure,  the  pressure  being 
effected  by  the  steam  generated  by  the  contact  of  the  hot  ore  and  the  chemical  solution 
in  a  closed  vessel. 

In  carrying  out  this  process  I  take  the  ore,  crushed  as  ordinarily  for  stamp-mill  or 
smelter,  and  heat  the  same  in  any  suitable  furnace  to  a  sufiicient  degree  and  for  a  proper 
time  to  desulphurize  it.  I  then  draw  the  ore,  while  at  red  heat,  into  an  iron  retort  of 
proper  strength  to  withstand  the  proposed  pressure,  and  provided  with  a  steam-tight 
door,  and  into  this  retort,  through  a  suitable  aperture,  after  closing  the  door,  I  introduce 
the  chemicals  in  a  state  of  solution,  the  steam  generated  creating  such  pressure  within 
the  retort  that  the  chemicals  are  forced  into  the  silica  or  rock  of  the  ore,  thoroughly 
disintegrating  the  same  and  freeing  the  metals  therefrom,  so  that  the  latter  are  ren- 
dered susceptible  of  ready  amalgamation.  The  process  will  be  facilitated  by  agitating 
the  retort. 

I  use  different  chemicals,  according  to  the  different  kinds  of  ore  to  be  treated,  and  the 
quantity  required  depends  upon  the  quantity  of  silica  or  other  refractory  substances  to 
be  decomposed  to  effect  a  thorough  disintegration  of  the  ore. 

For  the  treatment  of  most  of  the  refractory  ores  I  use  chloride  of  sodium  as  a  base, 
and  in  connection  therewith  nitrate  of  potash,  cyanide  of  sodium,  and  about  equal 
parts  of  sulphate  of  protoxide  of  iron  and  sulphate  of  copper,  the  proportions  being 
about  as  follows,  viz.:  chloride  of  sodium,  from  thirty  to  forty  pounds  to  the  ton ; 
nitrate  of  potassium,  from  one  to  two  pounds  to  the  ton  ;  cyanide  of  sodium,  from  two 
to  four  pounds  to  the  ton  ;  sulphate  of  protoxide  of  iron,  from  one  to  two  pounds  to  the 
ton  ;  sulphate  of  copper,  from  one  to  two  pounds  to  the  ton.  These  chemicals  are  to  be 
dissolved  in  boiling  or  hot  water  of  sufficient  quantity  to  cover  the  ore  in  the  retort.  If 
the  ores  to  be  treated  are  unusually  hard  or  refractory,  I  add  to  the  above  one  to  two 
pounds  of  hydrofluoric  acid,  or  one  to  two  pounds  of  fluoride  of  potassium  or  fluoride 
of  sodium,  according  to  the  character  of  the  ore.  After  the  ore  has  been  agitated  in  the 
retort  a  proper  time — say  from  ten  to  fifteen  minutes — under  from  fifty  to  one  hundred 
pounds  pressure  to  the  square  inch,  it  may  be  removed  while  hot  to  the  pulverizer,  then 
passed  through  any  convenient  and  desired  amalgamating  process. 

It  should  be  here  stated  that  while  the  ore  is  in  the  chemical  bath,  the  latter  acts  to 
disintegrate  the  ore  by  decomposing  or  destroying  the  silica  therein,  and  the  ore  is 
thoroughly  impregnated  with  the  chemicals,  thereby  effectually  disengaging  the  parti- 
cles of  metal  from  the  silica,  which,  if  not  disengaged,  will  not  amalgamate  with  the 
quicksilver  in  the  amalgamating-machines. 

To  facilitate  the  carrying  out  of  the  process,  I  prefer  to  use  a  cylindrical  retort 
mounted  on  axial  trunnions,  in  order  that  it  may  be  rotated  for  the  purpose  of  agitat- 
ing its  contents.  The  door  of  the  retort  should  be  in  its  side,  and  at  each  end  there 
should  be  a  projecting  coupling-nipple  provided  with  a  cut-off  cock,  to  which  may  be 
connected  pipes,  one  of  which  leads  from  the  top,  and  the  other  from  the  bottom,  of  an 
elevated  steam-tight  receiver  provided  with  safetj'-valve,  both  pipes  being  provided  with 
suitable  cocks.  The  chemical  solution  is  then  placed  in  the  elevated  cylinder,  and,  after 
the  retort  has  received  its  charge  of  heated  ore  and  been  closed,  the  pipes  from  the 
receiver  are  connected  to  the  coupling-nipples  and  the  cocks  all  opened.  The  solution 
will  flow  from  the  bottom  of  the  tank  to  the  retort,  and  the  steam  generated  in  the  latter 
will  flow  to  the  top  of  the  cylinder,  creating  a  pressure  therein  which  will  force  the  solu- 
tion rapidly  into  tne  retort.    After  the  pressure  has  decreased,  the  cocks  may  then  be 


PATENT-SPECIFICATIONS.  105 

closed,  the  pipes  disconnected  from  the  retort,  and  the  latter  rotated  for  the  purpose  of 
agitating  its  contents. 

The  apparatus  thus  partially  described  will  form  the  subject  of  a  separate  application 
for  Letters  Patent. 

I  do  not  confine  myself  to  the  chemicals  or  quantities  thereof  herein  enumerated,  as 
they  may  be  varied  as  required  by  the  character  of  the  ores  to  be  treated. 

I  am  aware  that  crushed  ores  have  been  subjected  to  the  action  of  chlorine  gas  under 
pressure,  and  that  unroasted  pulverized  ores  have  been  treated  with  chemical  solutions 
in  a  closed  vessel  under  pressure  created  by  the  injection  of  steam,  and  also  that  hot 
roasted  ores  have  been  treated  by  placing  cold  chemical  solutions  in  contact  therewith 
in  the  open  air,  or  not  under  pressure  ;  and  I  do  not  claim  any  of  such  modes  of  treat- 
ment. 

What  I  claim  is — 

1.  The  process  herein  described  for  separating  metals  from  ores,  the  same  consisting 
in  subjecting  hot  crushed  ores  to  the  action  of  disintegrating  chemicals  in  solution  under 
pressure,  the  pressure  being  effected  by  the  steam  generated  by  the  contact  of  the  hot 
ores  with  the  chemical  solution  in  a  closed  vessel,  substantially  as  specified. 

2.  The  process  herein  described  for  treating  refractory  ores  for  disengaging  the  precious 
metals  therefrom,  the  same  consisting  in  subjecting  hot  crushed  ores  to  the  action  of  a 
solution  of  chloride  of  sodium,  nitrate  of  potash,  cyanide  of  sodium,  sulphate  of  pro- 
toxide of  iron,  and  sulphate  of  copper,  under  pressure,  with  or  without  admixture  of 
hydrofluoric  acid,  fluoride  of  potassium,  or  fluoride  of  sodium,  the  pressure  being  effected 
by  the  steam  generated  by  the  contact  of  the  solution  with  the  hot  ore,  substantially  as 
set  forth. 

In  testimony  whereof  I  have  hereunto  set  my  hand  in  the  presence  of  two  subscrib- 
ing witnesses. 

HIRAM  W.  FAUCETT. 
"Witnesses : 

RoBT.  Harbison, 
Jno.  C.  Orrick. 


106  THE    CYANIDE    PROCESS. 

UNITED  STATES  PATENT  OFFICE. 


JOHN  F.  SANDERS,  of  Ogden,  Utah  Tbrritoey. 
COMPOSITION  FOR  DISSOLVING  THE  COATING  OF  GOLD  IN  ORE. 


Specification  forming  part  of  Letters  Patent  No.  244,080,  dated  July  12, 1881. 
(Application  filed  April  16, 1881.    No  specimens.) 

To  all  whom  it  may  concern. 

Be  it  known  that  I,  John  F.  Sanders,  of  Ogden,  in  the  county  of  Weber  and  Terri- 
tory of  Utah,  have  invented  an  improved  Composition  for  Dissolving  the  Coating  of 
Gold  in  Ore,  of  which  the  following  is  a  specification : 

The  coatings  that  envelop  gold  in  the  ore,  and  that  consist  usually  of  various  metallic 
oxides  and  of  silver,  have  thus  far  been  difficult  to  remove,  except  under  the  influence 
of  extreme  heat,  which  it  is  not  possible  at  all  places  to  apply,  or  by  the  waste  of  much 
valuable  time.  I  have  found  that  a  mixture  of  cyanide  of  potassium  and  phosphoric 
acid,  in  about  the  proportions  hereinafter  mentioned,  constitutes  a  powerful  solvent  for 
these  coatings  of  gold  ore.  . 

I  use  in  my  mixture  about  sixteen  parts  of  cyanide  of  potassium  to  one  part  glacial 
phosphoric  acid.  These  two  ingredients  I  mix  shortly  before  the  mixture  is  to  be  used. 
The  mixture  I  place  into  the  vessel  that  contains  the  covered  ore.  This  vessel  preferably 
is  a  rotating  barrel  made  of  iron  or  other  proper  material,  and  the  composition  above 
named  is  added  with  sufficient  water  to  form  a  thick  pulp  with  the  raw  gravel.  The 
proportions  of  my  improved  mixture  to  the  ore  will  vary,  of  course,  with  the  varying 
thickness  of  covering  of  the  gold.  They  will,  however,  be  readily  ascertained  by  testing 
with  samples  of  the  ore  to  be  treated.  The  barrel  is  rotated  or  agitated  in  suitable 
manner  for  from  fifteen  to  sixty  minutes,  as  may  be  required.  After  agitation  the  mixt- 
ure above  mentioned  will  be  found,  on  investigation,  to  have  dissolved  the  oxides  and 
the  sulphurous  coatings  of  the  ore,  and  the  agitation  of  the  barrel  or  vessel  removes  the 
dissolved  impurities,  leaving  the  gold  free  and  exposed,  and  permitting  it  to  be  amal- 
gamated by  the  addition  of  quicksilver,  in  the  usual  manner. 

The  amalgam  may  be  separated  from  the  impurities  which  have  joined  with  the 
improved  mixture  in  the  manner  in  which  amalgams  are  usually  separated  from 
impurities. 

I  am  aware  that  cyanides  have  already  been  used  in  the  extraction  of  gold ;  also,  that 
gold-bearing  ores  have  been  disintegrated  in  the  presence  of  heat  by  various  chemicals. 
This  I  do  not  claim.  By  using  phosphoric  acid  in  the  presence  of  cyanide  of  potassium 
1  am  enabled  to  dissolve  the  impurities  in  a  raw  state  and  with  great  rapidity. 

I  claim — 

The  composition  of  cyanide  of  potassium  and  phosphoric  acid,  in  about  the  pro- 
portions mentioned,  for  the  purpose  of  dissolving  the  impure  coatings  of  gold,  substan- 
tially  as  specified.  JOHN  F.  SANDERS. 

"Witnesses : 

Willy  G.  E.  Schultz, 
William  H.  C.  Smith. 


PATENT-SPECIFICATIONS.  107 

UNITED  STATES  PATENT  OFFICE. 


JEROME  "W.  SIMPSON,    of  Newark.  New  Jerskt. 
PROCESS  OF   EXTRACTING  GOLD,  SILVER,   AND   COPPER  FROM  THEIR   ORES. 


Specification  forming  part  of  Letters  Patent  No.  323,222,  dated  July  28,  1885. 
(Application  filed  October  20, 1884.    No  specimens.) 

To  all  whom  it  may  concern : 

Be  it  known  that  I,  Jerome  W.  Simpson,  a  citizen  of  the  United  States,  residing  at 
Newark,  in  the  county  of  Essex,  and  State  of  New  Jersey,  have  invented  certain  new 
and  useful  improvements  in  processes  of  extracting  gold,  silver,  and  copper  from  their 
ores;  and  I  do  hereby  declare  the  following  to  be  a  full,  clear,  and  exact  description  of 
the  invention,  such  as  will  enable  others  skilled  in  the  art  to  which  it  appertains  to 
make  and  use  the  same. 

The  object  of  this  invention  is  to  extract  certain  metals  from  their  ores  more  effect- 
ually and  at  a  reduced  cost;  and  it  consists  in  the  processes  hereinafter  set  forth,  and 
finally  embodied  in  the  clauses  of  the  claims. 

To  carry  my  invention  into  effect,  I  first  grind  or  crush  the  ore  containing  the  metal 
to  be  extracted  to  a  powder  of  more  or  less  fineness.  This  powder  is  then  treated  with 
certain  salts  in  solution  adapted  to  combine  chemically  witn  the  metal  in  said  ore  and 
form  therewith  a  soluble  salt.  After  thorough  agitation  to  mix  the  solution  with  the 
ore,  the  mixture  is  allowed  to  stand  until  the  solid  matter  is  settled  and  the  solution 
has  become  clear.  I  then  suspend  a  piece  or  plate  of  zinc  therein,  which  causes  the 
metal  dissolved  in  the  salt  solution  to  be  precipitated  thereon,  from  which  it  can  be 
removed  by  scraping  or  by  dissolving  the  zinc  in  sulphuric  or  hydrochloric  acid.  The 
precipitated  metal  may  then  be  melted  into  a  button. 

The  salt  solution  I  use  for  dissolving  the  metal  from  the  ore  is  composed  of  one  pound 
of  cyanide  of  potassium,  one  ounce  carbonate  of  ammonia,  one  half  ounce  chloride  of 
sodium,  and  sixteen  quarts  of  water,  or  other  quantities  in  about  the  same  proportions. 

This  solution  is  particularly  adapted  for  ores  containing  gold,  silver,  and  copper  in 
the  form  of  sulphurets. 

For  an  ore  containing  gold  and  copper  only  I  use  cj'^anide  of  potassium  and  carbonate 
of  ammonia  about  in  the  proportions  named. 

For  ores  rich  in  silver  I  employ  a  proportionately  larger  quantity  of  chloride  of 
sodium. 

I  am  aware  that  cyanide  of  potassium,  when  used  in  connection  with  an  electric 
current,  has  been  used  for  dissolving  metal,  and  also  that  zinc  has  been  employed  as  a 
precipitant,  and  the  use  of  these  I  do  not  wish  to  be  understood  as  claiming,  broadly. 

I  am  also  aware  that  carbonate  of  ammonia  has  been  employed  for  dissolving  such 
metals  as  are  soluble  in  a  solution  thereof,  and  the  use  of  this  I  do  not  claim;  but 

What  I  claim  as  new  is — 

1.  The  process  of  separating  gold  and  silver  from  their  ores,  which  consists  in  subject- 
ing the  ore  to  the  action  of  a  solution  of  cyanide  of  potassium  and  carbonate  of  ammonia, 
and  subsequently  precipitating  the  dissolved  metal,  substantially  as  set  forth 

2.  The  process  of  separating  metals  from  their  ores,  to  wit:  subjecting  the  ore  to  the 
action  of  a  solution  of  cyanide  of  potassium,  carbonate  of  ammonia,  and  chloride  o 
sodium,  and  subsequently  precipitating  the  dissolved  metals. 

In  testimony  that  I  claim  the  foregoing,  I  have  hereunto  set  my  hand  this  15th  day 
of  October,  1884. 

JEROME  W.  SIMPSON. 
"Witnesses: 

Oliver  Drake. 
Chablbb  H.  Pbi<i<. 


108  THE   CYANIDE   PROCESS. 

[Fifth  Edition.] 

No.  14,174.  A.  D.  1887. 

Date  of  application,  19th  Oct.,  1887;  complete  specification  left,  26th  July,  1888 — Accepted 

10th  Aug.,  1888. 

PROVISIONAL   SPECIFICATION. 


IMPROVEMENTS     IN     OBTAINING     GOLD    AND     SILVER    FROM     ORES    AND     OTHER 

COMPOUNDS. 

We,  John  Stewart  MacArthur,  Analytical  Chemist,  of  15  Princes  Street,  PoUokshields, 
in  the  County  of  Renfrew,  North  Britain,  Robert  Wardrop  Forrest,  M.D.,  and  William 
Forrest,  M.B.,  both  of  319  Crown  Street,  Glasgow,  in  the  County  of  Lanark,  North  Britain, 
do  hereby  declare  the  nature  of  this  invention  to  be  as  follows: 

This  invention  has  principally  for  its  object  the  obtaining  of  gold  from  its  ores  or 
other  compounds,  but  it  is  also  applicable  for  obtaining  silver  from  its  ores  or  com- 
pounds ;  and  it  comprises  an  improved  process,  which,  whilst  applicable  to  ores  or  com- 
pounds generally,  is  effectual  with  ores  and  compounds  from  which  gold  or  silver  have 
hitherto  not  been  easily  obtainable. 

In  carrying  out  the  invention  the  ore  or  other  compound  in  a  powdered  state  is  treated 
with  a  solution  containing  cyanogen  or  a  cyanide  (such  as  the  cyanides  of  potassium, 
sodium,  or  ammonium),  or  other  substance  or  compound  containing  or  yielding  cyanogen, 
till  all  or  nearly  all  of  the  gold  and  the  silver  are  dissolved;  the  operation  being  conducted 
in  a  wooden  vessel  or  a  vessel  made  of  or  lined  with  a  material  not  acted  on  to  any  consider- 
able extent  by  the  solution  or  substances  contained  therein.  The  solution  is  then  drawn 
off  and  the  metal  or  metals  are  recovered  by  any  suitable  process,  and  the  cyanogen, 
cyanide,  or  substance  containing  or  yielding  cyanogen  may  be  regenerated.  The  cyano- 
gen or  substance  containing  or  yielding  cyanogen  may  be  used  as  such,  or  such  materials 
may  be  taken  as  will  by  mutual  action  form  cyanogen  or  substances  containing  or  yield- 
ing same. 

Under  certain  circumstances  it  may  be  found  desirable  to  conduct  the  operation 
under  pressure,  in  which  case  a  closed  vessel  must  be  employed,  and  in  any  case,  if 
found  advisable,  such  operation  may  be  carried  on  under  varying  conditions  of  temper- 
Dated  this  19th  day  of  October,  1887. 

ALLISON  BROS., 
Agents  for  the  Applicants. 


COMPLETE  SPECIFICATION. 
Improvements  in  Obtaining  Gold  and  Silver  from  Ores  and  Other  Compounds. 

We,  John  Stewart  MacArthur,  Analytical  Chemist,  of  15  Princes  Street,  PoUokshields, 
in  the  County  of  Renfrew,  North  Britain,  Robert  Wardrop  Forrest,  M.D.,  and  William 
Forrest,  M.B.,  both  of  319  Crown  Street,  Glasgow,  in  the  County  of  Lanark,  North  Britain, 
do  hereby  declare  the  nature  of  this  invention,  and  in  what  manner  the  same  is  to  be 
performed,  to  be  particularly  described  and  ascertained  in  and  by  the  following  state- 
ment, that  is  to  say: 

This  invention  has  principally  for  its  object  the  obtaining  of  gold  from  its  ores  or 
other  compounds,  but  it  is  also  applicable  for  obtaining  silver  from  its  ores  or  com- 
pounds; and  it  comprises  an  improved  process,  which,  whilst  applicable  to  ores  or  com- 
pounds generally,  is  effectual  with  ores  and  compounds  from  which  gold  or  silver  have 
hitherto  not  been  easily  obtainable  because  of  the  presence  of  various  other  metals  or 
their  compounds,  or  because  of  the  physical  or  chemical  condition  of  the  gold  or  silver 
in  the  ores  or  compounds. 

In  carrying  out  the  invention  the  ore  or  other  compound  in  a  powdered  state  is  treated 
with  a  solution  containing  cyanogen  or  cyanide  (such  as  cyanide  of  potassium,  or  of 
sodium,  or  of  calcium),  or  other  substance  or  compound  containing  or  yielding  cyano- 
gen. In  practice  we  find  the  best  results  are  obtained  with  a  very  dilute  solution,  or  a 
solution  containing  or  yielding  an  extremely  small  quantity  of  cyanogen  or  a  cyanide, 
such  dilute  solution  having  a  selective  action  such  as  to  dissolve  the  gold  or  silver  in 
preference  to  the  baser  metals.  In  preparing  the  solution  we  proportion  the  cyanogen 
to  the  quantity  of  gold  or  silver  or  gold  and  silver  estimated  by  assay  or  otherwise  to  be 
in  the  ore  or  compound  under  treatment,  the  quantity  of  a  cyanide  or  cyanogen-yielding 
substance  or  compound  being  reckoned  according  to  its  cyanogen.  We  mix  the  pow- 
dered ore,  or  compound,  with  the  solution  in  a  vessel  made  of  or  lined  with  wood  or  any 
other  convenient  material  not  appreciably  acted  on  by  the  solution.    The  process  is 


PATENT-SPECIFICATIONS.  109 

expedited  by  stirring  the  mixture  of  ore  and  solution  intermittently,  or  continuously 
for  which  purpose  any  convenient  mechanical  agitator  may  be  fitted  to  the  vessel 
When  all  or  nearly  all  the  gold  or  silver  is  dissolved  the  solution  is  drawn  off  from  the 
ore  or  undissolved  residue,  and  is  treated  in  any  suitable  known  way,  as  for  example 
with  zinc,  for  recovering  the  gold  and  silver.  The  residuary  cyanogen  compounds  may 
also  be  treated  by  known  means  for  regeneration  or  reconversion  into  a  condition  in 
which  they  can  be  used  for  treating  fresh  charges  of  ores  or  compounds. 

Any  cyanide  soluble  in  water  may  be  used,  such  as  ammonium,  barium,  calcium, 
potassium,  or  sodium  cyanide,  or  a  mixture  of  any  two  or  more  of  them,  or  any  mixture 
of  materials  may  be  taken  which  will,  by  mutual  action,  form  cyanogen,  or  a  substance 
or  substances  containing  or  yielding  cyanogen. 

In  dealing  with  ores  or  compounds  containing,  per  ton,  twenty  ounces  or  less  of  gold 
or  silver,  or  gold  and  silver,  we  generally  use  a  (Quantity  of  cyanide,  the  cyanogen  of 
which  is  equal  in  weight  to  from  one  to  four  parts  in  every  thousand  parts  of  the  ore  or 
compound,  and  we  dissolve  the  cyanide  in  a  quantity  of  water  of  about  half  the  weight 
of  the  ore.  In  the  case  of  richer  ores  or  compounds,  whilst  increasing  the  quantity  of 
cyanide  to  suit  the  greater  quantitj'^  of  gold  or  silver,  we  also  increase  the  quantity  of 
water  so  as  to  keep  the  solution  dilute.  In  using  free  cyanogen,  the  cyanogen  obtained 
as  a  gas  in  any  well  known  way  is  led  into  water  to  form  the  solution  to  be  used  in  our 
process;  or  any  suitable  known  mode  of  setting  cyanogen  free  in  solution  may  be 
employed. 

In  some  circumstances  it  may  be  found  desirable  to  conduct  the  operation  under 
pressure  in  a  closed  vessel ;  and  a  higher  than  the  ordinary  temperature  may  be  used  if 
found  desirable. 

Having  now  particularly  described  and  ascertained  the  nature  of  our  said  invention 
and  in  what  manner  the  same  is  to  be  performed,  we  declare  that  what  we  claim  is — 

1.  The  jjrocess  of  obtaining  gold  and  silver  from  ores  and  other  compounds,  consisting 
in  dissolving  them  out  by  treating  the  powdered  ore  or  compound  with  a  solution  con- 
taining cyanogen  or  a  cyanide  or  cyanogen-yielding  substance,  substantially  as  herein- 
before described. 

2.  The  process  of  obtaining  gold  and  silver  from  ores  and  other  compounds,  consisting 
in  dissolving  them  out  by  treating  the  powdered  ore  or  compound  with  a  dilute  solution 
containing  a  quantity  of  cyanogen  or  a  cyanide  or  cyanogen-yielding  substance,  the 
cyanogen  of  which  is  proportioned  to  the  gold  or  silver  or  gold  and  silver,  substantially 
as  hereinbefore  described. 

Dated  this  16th  day  of  July,  1888. 

ALLISON  BROS., 
Agents  for  the  Applicants. 


110  THE    CYANIDE    PROCESS. 

UNITED   STATES   PATENT   OFFICE. 


JOHN  STEWART  MacARTHUR,  of  Pollokshiblds,  County  of  Renfrew,  and  ROB- 
ERT W.  FORREST  AND  WILLIAM  FORREST,  of  Glasgow,  County  of  Lanark 
Scotland. 

PROCESS  OF  OBTAINING  GOLD  AND  SILVER  FROM  ORES. 


Specification  forming  part  of  Letters  Patent  No.  403,202,  dated  May  14,  1880. 

(Application  filed  November  9, 1887.  Serial  No.  254,699.  (No  specimens.)  Patented  in  England, 
October  19, 1887,  No.  14,174;  in  Cape  of  Good  Hope,  January  7,  1888,  No.  6-101;  in  Victoria,  Jan- 
uary 19, 1888,  No.  5,572;  in  New  South  Wales,  January  21, 188^1,  No.  453:  in  South  Australia,  Jan- 
uary 2,'?,  1888,  No.  948;  in  Tasmania,  January  24,  1888,  No.  529;  in  New  Zealand,  February  1, 1888, 
No.  2,775;  in  Canada,  February  6, 1888,  No.  28,471;  in  France,  April  6,  1888,  No.  189,808;  In  Bel- 
glum,  July  24, 1888,  No.  82,673;  in  Brazil,  August  23,  1888,  No.  619;  in  Portugal,  August  30, 1888, 
No.  1,272;  in  Italy,  September  30, 1888,  No.  23,852,  and  in  Spain,  October  2, 1888,  No.  8,538.) 

To  all  whom  it  may  concern: 

Be  it  known  that  we,  John  Stewart  MacArthur,  a  subject  of  the  Queen  of  Great  Brit- 
ain, residing  at  15  Princes  Street,  Pollokshields,  in  the  County  of  Renfrew,  Scotland, 
and  Robert  Wardrop  Forrest  and  William  Forrest,  both  subjects  of  the  Queen  of  Great 
Britain,  residing  at  319  Crown  Street,  Glasgow,  in  the  County  of  Lanark,  Scotland,  have 
invented  certain  new  and  useful  Improvements  in  Processes  of  Obtaining  Gold  and  Sil- 
ver from  Ores  (for  which  we  have  obtained  patents  in  the  following  countries:  Great 
Britain,  No.  14,174,  dated  October  19,  1887;  Cape  of  Good  Hope,  No.  6-101,  dated  January  7, 
1888;  Victoria,  No.  5,572,  dated  January  19,  1888;  New  South  Wales,  No.  453,  dated  Jan- 
uary 2i,  1888;  South  Australia,  No.  948,  dated  January  23,  1888;  Tasmania,  No.  529,  dated 
January  24,  1888;  New  Zealand,  No.  2,775,  dated  February  1,  1888;  Canada,  No.  28,471, 
dated  February  6, 1888;  France,  No.  189,808,  dated  April  6,  1888;  Belgium,  No.  82,673,  dated 
July  24,  1888;  Brazil,  No.  619,  dated  August  23,  1888;  Portugal,  No.  1,272,  dated  August  30, 
1888;  Italy,  No.  23,852,  dated  September  30,  1888,  and  Spam,  No.  8,538,  dated  October  2, 
1888) ;  and  we  do  hereby  declare  that  the  following  is  a  full,  clear,  and  exact  description 
of  the  invention,  which  will  enable  others  skilled  in  the  art  to  which  it  appertains  to 
make  and  use  the  same. 

This  invention  has  principally  for  its  object  the  obtaining  of  gold  from  ores;  but  it  is 
also  applicable  for  obtaining  silver  from  ores  containing  it,  wnether  with  or  without 
gold,  and  it  comprises  an  improved  process  which,  while  applicable  to  auriferous  and 
argentiferous  ores  generally,  is  advantageously  and  economically  effective  with  refrac- 
tory ores,  or  ores  from  which  gold  and  silver  have  not  been  satisfactorily  or  profitably 
obtainable  by  the  amalgamating  or  other  processes  hitherto  employed,  such  as  ores  con- 
taining sulphides,  arsenides,  tellurides,  and  compounds  of  base  metals  generally,  and 
ores  from  which  the  gold  has  not  been  easily  or  completely  separable  on  account  of  its 
existing  in  the  ores  in  a  state  of  extremely  fine  division. 

The  invention  consists  in  subjecting  the  auriferous  or  argentiferous  ores  to  the  action 
of  a  solution  containing  a  small  quantity  of  a  cyanide,  as  hereinafter  set  forth,  without 
any  other  chemically-active  agent,  such  quantity  of  cyanide  being  reckoned  according 
to  its  cyanogen,  and  the  cyanogen  being  proportioned  to  the  quantity  of  gold  or  silver, 
or  gold  and  silver,  estimated  by  assay  or  otherwise  to  be  in  the  ores  under  treatment. 
By  treating  the  ores  with  the  dilute  and  simple  solution  of  a  cyanide  the  gold  or  silver  is, 
or  the  gold  and  silver  are,  obtained  in  solution,  while  any  base  metals  in  the  ores  are  left 
undissolved,  except  to  a  practically  inappreciable  extent,  whereas  when  a  cyanide  is 
used  in  combination  with  an  electric  current  or  in  conjunction  with  another  chemically- 
active  agent— such  as  carbonate  of  ammonium,  or  chloride  of  sodium,  or  phosphoric 
acid— or  when  the  solution  contains  too  much  cyanide,  not  only  is  there  a  greater  expendi- 
ture of  chemicals  in  the  first  instance,  but  the  base  metals  are  dissolved  to  a  large  extent 
along  with  the  gold  or  silver,  and  for  their  subsequent  separation  involve  extra  expense, 
which  is  saved  by  our  process. 

In  practically  carrying  out  our  invention  we  take  the  ore  in  a  powdered  state  and  mix 
with  it  the  solution  of  a  cyanide  in  a  vessel  made  of  or  lined  with  any  material  not 
appreciably  acted  on  by  the  solution.  We  employ  a  vessel  made  of  or  lined  with  wood; 
but  it  may  be  made  of  or  lined  with  any  ordinary  inert  material — such  as  stone,  brick, 
slate,  rubber,  gutta-peiicha,  cement,  glass,  earthenware,  iron  (plain,  tinned,  or  enameled), 
or  lead.  The  process  is  expedited  by  stirring  or  triturating  the  mixture  of  ore  and  solu- 
tion intermittently  or  continuously,  for  which  purpose  any  convenient  mechanical 
agitator  may  be  fitted  to  the  vessel.  A  pan-mill  with  edge  runners  or  other  known  trit- 
urating device  may  be  advantageously  used.  The  solution  is  allowed  to  act  on  the  ore 
until  the  gold  or  silver  is  all  or  nearly  all  dissolved,  and  the  solution  is  then  drawn  off 
from  the  ore  or  undissolved  residue. 

Any  cyanide  soluble  in  water  may  be  used — such  as  ammonium,  barium,  calcium,, 
potassium,  or  sodium  cyanide,  or  a  mixture  of  any  two  or  more  of  them.  We  regulate 
the  quantity  of  cyanide  so  that  its  cyanogen  will  be  in  proportion  to  the  quantity  of 


PATENT-SPECIFICATIONS.  Ill 

gold  or  silver  or  gold  and  silver  in  the  charge  of  ore;  but  in  all  cases  we  dissolve  it  in 
suflBcient  water  to  keep  the  solution  extremely  dilute,  because  it  is  when  the  solution  is 
dilute  that  it  has  a  selective  action  such  as  to  dissolve  the  gold  or  silver  in  preference  to 
the  baser  metals. 

In  dealing  with  ores  containing  per  ton  twenty  ounces  or  less  of  gold  or  silver  or  gold 
and  silver,  we  find  it  most  advantageous  to  use  a  quantity  of  cyanide  the  cyanogen  of 
which  is  equal  in  weight  to  from  one  to  four  parts  for  every  thousand  parts  of  the 
ore,  and  we  dissolve  the  cyanide  in  a  quantity  of  water  of  about  half  the  weight  of  the 
ore.  We  generally  use  a  solution  containing  two  parts  of  cyanogen  for  every  thousand 
parts  of  the  ore.  In  the  case  of  richer  ores,  while  increasing  the  quantity  of  cyanide  to 
suit  the  greater  quantity  of  gold  or  silver,  we  also  increase  the  quantity  of  water  so  as 
to  keep  the  solution  dilute.  In  other  words,  the  cyanide  solution  should  contain  from 
two  to  eight  parts,  by  weight,  of  cyanogen  to  one  thousand  parts  of  water,  and  the 
quantity  of  the  solution  used  should  be  determined  by  the  ricnness  of  the  ore.  After 
the  solution  has  been  decanted  or  separated  from  the  undissolved  residues  the  gold  and 
silver  may  be  obtained  from  it  in  any  convenient  known  way — such  as  evaporating  the 
solution  to  dryness  and  fusing  the  resulting  saline  residue,  or  by  treating  the  solution 
with  sodium  amalgam. 

Having  fully  described  our  invention,  what  we  desire  to  claim  and  secure  by  Letters 
Patent  is — 

The  process  of  separating  precious  metal  from  ore  containing  base  metal,  which  process 
consists  in  subjecting  the  powdered  ore  to  the  action  of  a  cyanide  solution  containing 
cyanogen  in  the  proportion  not  exceeding  eight  parts  of  cyanogen  to  one  thousand  parts 
of  water. 

JOHN  STEWART  MacARTHUR. 
ROBT.  W.  FORREST. 
W.  FORREST. 
Witnesses: 

robt.  dunlop, 
William  Brunton, 

Law  clerks,  both  of  160  West  George  Street,  Glasgow. 


112  THE   CYANIDE    PROCESS. 

UNITED   STATES   PATENT   OFFICE. 


JOHN  STEWART  MacARTHUR,  of  Pollokshields,  County  of  Rknfekw,  Scotland. 

METALLURGICAL   FILTER. 


Specification  forming  part  of  Letters  Patent  No.  418,138,  dated  December  24,  1889. 

(Application  filed  November  13, 1889.    Serial  No.  330,195.    No  model.) 

To  all  whom  it  may  concern : 

Be  it  known  that  I,  Jotin  Stewart  MacArthur,  a  subject  of  the  Queen  of  Great  Britain, 
residing  at  Pollokshields,  in  the  county  of  Renfrew,  Scotland,  have  invented  a  new  and 
useful  Improvement  in  Metallurgical  Filters,  of  which  the  following  is  a  specification: 

This  invention  relates  to  a  filter  for  precipitating  and  separating  precious  metals  from 
solutions  containing  them — such,  for  instance,  as  chlorides,  bromides,  theosulphates 
(sometimes  called  "hyposulphites"),  or  sulphates  obtained  in  the  well-known  Plattner, 
von  Patera,  Russell,  Ziervogel,  and  Augustine  extracting  processes. 

The  object  of  the  invention  is  to  provide  a  filter  having  a  large  active  surface  for  the 
metals  in  solution. 

In  the  accompanying  drawings.  Figure  1  is  a  sectional  elevation  of  a  series  of  these 
improved  filters.  Fig.  2  is  a  longitudinal  vertical  section  of  a  filtering  apparatus  com- 
prising two  of  these  improved  filters  constructed  in  modified  form.  Fig.  3  represents  a 
zinc  filiform  sponge,  constituting  the  principal  feature  of  this  improved  filter,  the  fila- 
ments of  the  sponge  being  represented  on  an  enlarged  scale. 

Similar  numerals  of  reference  indicate  corresponding  parts  in  the  different  figures. 

This  improved  filter  comprises  a  containing-vessel  10  and  a  zinc  sponge  11,  disposed 
therein.  The  zinc  sponge  is  preferably  supported  on  a  perforated  false  oottom  12,  dis- 
posed within  said  vessel  near  the  bottom  proper  thereof.  The  vessel  is  provided  with  an 
inlet-tube  13  and  an  outlet-tube  14,  the  inlet-tube  being  preferably  disposed  near  the 
bottom  of  the  vessel  and  the  outlet-tube  near  the  top  thereof,  each  of  said  tubes  being 
provided  with  a  coupling-nut  15  when  the  vessels  are  used  in  series. 

A  number  of  these  filters  are  preferably  arranged  in  series,  as  represented  in  Fig.  1, 
from  six  to  ten  being  ordinarily  employed.  When  so  arranged,  the  filters  are  connected 
by  pipes  16,  which  extend  from  the  outlet  near  the  top  of  one  vessel  to  the  inlet  near  the 
bottom  of  the  adjacent  vessel.  A  reservoir  or  tank  17  for  containing  the  solution  hold- 
ing the  precious  metals  is  disposed  adjacent  to  the  first  filter  of  the  series  and  elevated 
a  sufficient  distance  to  secure  a  proper  flow  of  the  liquid  through  the  filters.  This  tank 
is  provided  with  an  outlet-tube  18  near  its  bottom,  said  tube  being  provided  with  a  stop- 
cock 19,  and  connected  by  pipe  20  with  the  inlet-tube  of  the  first  filter  of  the  series.  The 
zinc  sponge,  which  constitutes  the  filtering  material  and  precipitant,  is  preferably  com- 
posed of  fine  threads  or  filaments  of  zinc  interlocked  together.  The  zinc  threads  from 
which  the  sponge  is  formed  are  cut  by  a  turning  tool  from  a  series  of  zinc  disks  held  be- 
tween lathe-centers  and  turned ;  or  the  zinc  sponge  may  be  formed  by  passing  molten 
zinc,  at  a  temperature  just  above  the  melting-point,  through  a  fine  sieve  and  allowing 
it  to  fall  into  water.  This  improved  zinc  sponge  presents  a  very  large  contact-sur- 
face for  the  action  of  the  solution,  and  it  does  not  become  easily  choked.  Each  contain- 
ing-vessel may  be  provided  with  a  vertical  partition  or  partitions  21,  as  illustrated  in 
Fig.  2,  whereby  the  vessel  is  divided  into  two  or  more  compartments  or  filtering-cham- 
bers. These  partitions  extend  to  a  point  near  the  bottom  or  top  of  the  vessel,  as  the  case 
may  be,  or  they  are  provided  with  holes  near  the  top  or  near  the  bottom  of  the  vessel. 
In  case  the  vessel  has  three  or  more  filtering-chambers,  the  partitions  are  provided  with 
communicating-openings,  disposed  alternately  near  the  bottom  and  top  of  the  vessel, 
whereby  the  passage  of  the  solution  is  downward  through  one  of  the  filtering-chambers, 
upward  through  the  adjoining  filtering-chamber,  and  downward  again  through  the 
third  filtering-chamber,  and  so  on. 

In  the  use  of  this  improved  filtering  apparatus  the  solution  containing  the  precious 
metal  is  placed  in  the  tank  17  and  the  cock  19  is  opened.  In  case  a  series  of  separate 
filters  is  employed,  as  represented  in  Fig.  1,  the  solution  passes  from  the  tank  through 
the  pipe  20  and  into  the  first  filter  of  the  series,  near  the  bottom  thereof,  beneath  the 
false  bottom  12,  thence  upward  through  the  zinc  sponge  within  the  filter,  thence  out- 
ward near  the  top  of  the  first  filter,  thence  through  the  connecting-pipe  to  the  next  filter 
of  the  series,  where  it  again  enters  near  the  bottom  and  passes  upward  through  the  zinc 
sponge  to  the  top  of  the  second  filter  of  the  series,  and  so  on.  The  metal  which  is  not 
precipitated  by  the  first  filter  is  caught  in  the  zinc  sponge  of  the  su-cceeding  filters  of 
the  series. 

In  case  filters  having  a  number  of  compartments  are  employed,  the  solution  is  perfer- 
ably  admitted  to  the  first  compartment  at  the  top  thereof,  and  passes  down  through  the 
zinc  sponge  contained  in  said  compartment  to  near  the  bottom  thereof,  and  thence 
passes  into  the  second  compartment  and  upward  through  the  zinc  sponge  therein  con- 
tained to  near  the  top  of  said  compartment,  and  thence  downward  through  the  next 


PATENT-SPECIFICA.TIONS. 


113 


(No  Model.) 


No.  418.138. 


J.  S.  MacARTHUR. 

METALLURGICAL  FILTER. 

Patented  Deo.  24,  1889. 


T^cy  d. 


WITJVESS£S 


IJVVEJ^rTOE 


^€<:^ 


Attorney 


8cp 


114  THE   CYANIDE   PROCESS. 

compartment,  and  so  on  through  the  several  compartments  of  the  compound  filter,  and 
thence  to  the  next  compound  filter  of  the  series  and  through  its  several  compartments. 
The  precious  metal  may  be  separated  from  the  zinc  sponge  by  distillation,  or  the  zinc 
sponge  containing  the  precious  metal  may  be  placed  in  a  suitable  sieve  and  subjected  to- 
a  screening  operation,  preferably  under  water.  In  this  operation  the  greater  part  of  the 
precious  metal  will  pass  through  the  sieve  and  the  greater  part  of  zinc  sponge  will 
remain  therein. 
I  claim  as  my  invention — 

1.  A  metallurgical  filter  for  separating  a  precious  metal  from  a  solution  containing 
said  metal,  consisting  of  a  vessel  provided  with  inlet  and  outlet  openings,  and  a  zinc 
sponge  disposed  in  said  vessel  between  said  openings,  substantially  as  described. 

2.  A  metallurgical  filter  for  separating  a  precious  metal  from  a  solution  containing 
said  metal,  consisting  of  a  vessel  provided  with  inlet  and  outlet  openings  and  a  filiform 
zinc  sponge  disposed  in  said  vessel  between  said  openings,  substantially  as  described. 

3.  A  metallurgical  filter  for  separating  a  precious  metal  from  a  solution  containing 
said  metal,  consisting  of  a  vessel  provided  with  a  perforated  false  bottom,  a  zinc  sponge 
within  said  vessel  above  said  false  bottom,  and  inlet  and  outlet  openings  above  and 
below  said  sponge,  substantially  as  described. 

4.  A  metallurgical  filter  for  separating  a  precious  metal  from  a  solution  containing- 
said  metal,  consisting  of  a  vessel  provided  with  a  perforated  false  bottom,  a  filiform  zinc 
sponge  within  said  vessel  above  said  false  bottom,  and  inlet  and  outlet  openings  above 
and  below  said  filiform  sponge,  substantially  as  described. 

5.  A  nietallurgical  filtering  apparatus  for  separating  a  precious  metal  from  a  solution 
containing  said  metal,  consisting  of  a  series  of  vessels,  a  zinc  sponge  in  each  of  said  ves- 
sels, pipes  connecting  the  outlet-tube  of  one  vessel  of  the  series  with  the  inlet-tube  of  the 
adjacent  vessel  of  the  series,  and  a  reservoir  for  supplying  the  solution  to  the  first  vessel 
of  the  series,  substantially  as  described. 

6.  A  metallurgical  filtering  apparatus  for  separating  a  precious  metal  from  a  solution 
containing  said  metal,  consisting  of  a  series  of  vessels,  each  of  which  has  an  inlet-tube 
near  its  bottom,  an  outlet-tube  near  its  top,  and  a  perforated  false  bottom  above  the 
inlet-tube,  zinc  sponges  disposed  in  the  several  vessels,  pipes  connecting  the  inlet  and 
outlet-tubes  of  the  several  vessels,  and  a  reservoir  for  supplying  the  solution  to  the  first 
vessel  of  the  series,  substantially  as  described. 

7.  A  metallurgical  filter  for  separating  a  precious  metal  from  a  solution  containing 
said  metal,  consisting  of  a  vessel  provided  with  a  partition  dividing  said  vessel  into  a 
plurality  of  filtering-chambers,  said  partition  being  provided  with  openings  near  one 
end,  and  zinc  sponges  disposed  in  said  compartments,  substantially  as  described. 

JOHN  STEWART  MacARTHUR. 

Witnesses: 

F.  C.  Somes. 
Gordon  Wilson,  Je. 


PATENT-SPECIFICATIONS.  115 

UNITED   STATES   PATENT   OFFICE. 


JOHN  STEWART  MacARTHUE,  of  Pollokshields,  County  of  Renfrew,  and 
ROBERT  WARDROP  FORREST  and  WILLIAM  FORREST,  of  Glasgow,  County 
OF  Lanark,  Assignors  to  the  CASSEL  GOLD  EXTRACTING  COMPANY 
(Limited)  of  Glasgow,  Scotland. 

PROCESS  OF  SEPARATING  GOLD  AND  SILVER  FROM  ORE. 


Specification  forming  part  of  Letters  Patent  No.  418,137,  dated  December  24, 1889. 

(Application  filed  April  4, 1889.  Serial  No.  305,998.  [Specimens.]  Patented  in  Natal,  September  11, 
1888,  No.  32;  in  New  South  Wales,  September  27,  1888,  No.  965,  and  in  Tasmania,  September  29, 
1888,  No.  609.) 

To  all  whom  it  may  concern: 

Be  it  known  that  we,  John  Stewart  MacArthur,  residing  at  Pollokshields,  in  the 
county  of  Renfrew,  and  Robert  Wardrop  Forrest  and  William  Forrest,  both  residing  at 
Glasgow,  in  the  county  of  Lanark,  Scotland,  all  subjects  of  the  Queen  of  Great  Britain, 
have  invented  certain  new  and  useful  improvements  in  the  process  of  separating  gold 
and  silver  from  ores  (for  which  we  have  received  Letters  Patent  in  Natal,  No.  32,  dated 
September  11,  1888 ;  New  South  Wales,  No.  965,  dated  September  27,  1888,  and  Tasmania, 
No.  609,  dated  September  29,  1888) ;  and  we  do  hereby  declare  that  the  following  is  a  full, 
clear,  and  exact  description  of  the  invention,  which  will  enable  others  skilled  in  the  art 
to  which  it  appertains  to  make  and  use  the  same. 

This  invention  relates  to  an  improvement  in  the  process  of  separating  precious  metals 
from  ores  described  in  Letters  Patent  of  the  United  States,  No.  403,202,  granted  to  us 
May  14,  1889.  In  that  process  a  cyanide  is  used  as  the  separating  agent,  and  it  has  been 
found  tRat  ores  containing  pyrites  or  sulphurets  which  have  been  exposed  to  the 
weather  and  become  partially  oxidized  absorb  a  comparatively  large  quantity  of  the 
cyanide. 

'The  object  of  this  invention  is  to  economize  the  process  by  preventing  the  absorption 
of  the  cyanide. 

The  invention  consists  in  separating  precious  metals  from  ores  by  first  nevitralizing 
the  ore  by  the  addition  of  an  alkali  or  alkaline  earth  and  then  leaching  such  prepared 
charge  with  a  cyanide  solution. 

In  carrying  out  the  first  or  preparatory  step  of  this  improved  process,  we  take  ore 
containing  iron  pyrites  or  other  compound  which  has  become  partially  oxidized  by 
exposure  to  the  weather  and  mix  with  it,  when  in  a  powdered  state,  a  sufficient  quan- 
tity of  potash,  lime,  or  other  alkali  or  alkaline  earth,  to  neutralize  the  salts  of  iron  or 
other  objectionable  ingredients  formed  by  the  partial  oxidation. 

The  quantity  of  alkali  or  alkaline  earth  to  be  employed  will  depend  upon  the  nature 
of  the  ore,  and  must  be  determined  by  first  taking  a  test  quantity  of  the  particular  ore 
to  be  treated  and  adding  the  alkali  or  alkaline  earth  thereto  until  the  alkali  ceases  to  be 
absorbed.  When  this  condition  is  reached  the  liquid  will  cause  red  litmus-paper  to 
turn  blue.  The  proportion  of  the  alkali  or  alkaline  earth  so  absorbed  will  indicate  the 
proper  proportion  thereof  to  be  added  to  the  bulk  of  the  ore  to  be  treated.  In  case  lime 
is  employed,  1  per  cent  of  the  alkali  to  99  per  cent  of  ore  will  generally  be  found  suffi- 
cient. After  this  prejiaratory  treatment  the  ore  (which  may  consist  of  tailings  or  resi- 
dues from  other  processes  or  operations)  is  treated  with  the  cyanide  solution  by  being 
agitated  therewith  or  by  being  ground  therewith  in  a  pan-mill  or  other  suitable  grind- 
ing-mill ;  or,  as  we  find  preferable  in  the  case  of  some  ores,  the  cyanide  solution  maj'  be 
made  to  percolate  through  said  ores  one  or  more  times  until  all  or  nearly  all  the 
precious  metals  are  dissolved.  For  this  percolation  very  simple  tanks,  vats,  or  vessels 
may  be  used,  such  vessels  being  provided  with  permeable  false  bottoms  or  any  suitable 
filtering  apparatus.  The  cyanide  solution  containing  the  gold  or  silver  is  next  made  to 
pass  through  a  sponge  of  zmc,  whereby  said  metal  is  precipitated  from  the  solution  and 
retained  in  the  sponge.  The  zinc  sponge  is  preferably  composed  of  fine  threads  or  fila- 
ments of  zinc.  These  zinc  threads  are  formed  in  shavings  cut  by  a  turning  tool  from 
a  series  of  zinc  disks  held  in  a  lathe  ;  or  the  sponge  may  be  formed  by  passing  molten 
zinc  at  a  temperature  just  above  the  melting  point  through  a  fine  sieve  and  allowing  it 
to  fall  into  the  water.  The  sponge  thus  formed  presents  a  very  large  contact  surfacelor 
the  solution,  and  it  does  not  oecome  easily  choked. 

The  precious  metals  maybe  separated  from  the  zinc  sponge  by  distillation;  or  the 
zinc  sponge  containing  the  precious  metal  may  be  placed  in  a  suitable  sieve  and  sub- 
jected to  a  screerrtng  operation,  preferably  under  water.  In  this  operation  the  greater 
part  of  the  precious  metal  will  pass  through  the  sieve  and  the  greater  part  of  the  zinc 
sponge  will  remain  therein. 


116  THE    CYANIDE    PROCESS. 

We  claim  as  our  invention — 

1.  The  process  of  separating  precious  metals  from  an  ore,  which  consists  in  neutraliz- 
ing the  ore  by  the  addition  of  an  alkali  or  alkaline  earth,  and  then  leaching  the  neu- 
tralized ore  with  a  cyanide  solution. 

2.  The  process  of  separating  precious  metal  from  an  ore,  which  consists  in  neutralizing 
the  ore  by  the  addition  of  an  alkali  or  alkaline  earth,  then  leaching  the  neutralized  ore 
with  a  cyanide  solution,  and  then  passing  the  cyanide  solution  containing  the  precious 
metal  through  a  sponge  of  zinc,  substantially  as  set  forth. 

JOHN    STEWART   MacARTHUR. 
ROBERT  WARDROP   FORREST. 
WILLIAM  FORREST, 
Witnesses : 

Robert  Jamikson  MacKinlat, 
Chaeles  Keith  Ritchie, 
Both  of  160  West  George  Street,  Glasgow,  Clerks  at  Law. 


PATENT-SPECIFICATIONS.  117 

UNITED   STATES    PATENT   OFFICE. 


EDWARD  D.  KENDALL,  of  Brooklyn,  New  York. 
COMPOSITION  OF  MATTER  FOR  THE  EXTRACTION  OF  GOLD  AND  SILVER  FROM  ORES. 


Specification  forming  part  of  Letters  Patent  No.  482,577,  dated  September  13,  1892. 
(Application  filed  May  27, 1892.    Serial  No.  434,528.    No  specimens.) 

To  all  whom  it  may  concern: 

Be  it  loiown  that  I,  Edward  D.  Kendall,  a  citizen  of  the  United  States,  residing  at 
Brooklyn,  in  the  county  of  Kings  and  State  of  New  York,  have  invented  a  new  and  use- 
ful composition  of  matter  to  be  used  for  the  extraction  of  gold  and  silver  from  ores, 
so-called  "tailings,"  and  other  matters  containing  one  or  both  of  these  metals,  of  whicli 
composition  the  following  is  a  specification. 

My  composition  consists  of  the  following  ingredients,  combined  as  hereinafter  stated  : 
water  (hot  or  cold),  potassium  ferricyanide  (or  other  soluble  ferricyanide),  and  potas- 
sium cyanide  (or  other  soluble  cyanide).  The  best  proportions  of  the  two  last  men- 
tioned constituents  vary  somewhat  with  the  different  ferricyanides  and  cyanides,  and 
may  be  determined  by  calculation  based  on  the  molecular  weights  of  the  salts  or  the 
chemical  equivalents  of  their  elements,  and  also  by  considering  that  the  purpose  of  my 
composition  is  to  set  free  cyanogen  to  form — for  example,  when  the  potassium  salts  are 
used — the  soluble  double  cyanide  of  gold  or  silver  and  potassium,  and  by  applying  my 
theory  of  the  chemical  reactions  which  occur,  set  forth  in  the  following  formula: 

4  Kg  (CslSra)^  Fe2  + 16  KCN  +  8  Au  =  4  Kg  (CsNa)^  Fez  -f  8  K  Au  (CN)2. 

The  indicated  proportions  are  therefore,  practically,  by  weight,  two  and  one  half  parts 
of  potassium  ferricyanide  and  one  part  oi  potassium  cyanide,  and  these  proportions  I 
have  found  satisfactory  in  practice ;  but  they  may  be  varied  within  wide  limits  without 
departing  from  my  invention.  The  potassium  ferricyanide,  which  is  a  product  of  the 
chemical  action,  facilitates  the  solution  of  the  resulting  cyanides,  and  after  the  separa- 
tion of  the  precious  metal  from  the  menstruum  by  appropriate  means,  may  be  utilized 
by  a  process  which  I  propose  to  make  the  subject  of  a  separate  application. 

To  prepare  my  composition,  I  dissolve  the  ferrocyanide  in  one  portion  of  water  and 
the  cyanide  in  another  portion,  and  mix  the  two  solutions ;  or  either  salt,  in  solid  form, 
may  by  added  to  the  solution  of  the  other.  In  dissolving  the  salts  I  do  not  always 
confine  myself  to  a  specific  proportion  of  water.  More  or  less  water  may  be  used.  As 
a  rule,  the  more  concentrated  the  composition  the  more  energetic  its  action,  but  the 
more  costly.  Except  in  treating  substances  very  rich  in  gold  or  silver,  my  composition 
will  always  be  used  in  a  more  or  less  dilute  condition. 

In  using  the  herein-described  composition,  the  gold-  and  silver-bearing  minerals,  tail- 
ings, and  other  matters,  cold  or  while  moderately  heated,  with  or  without  prior  chemical 
or  mechanical  treatment,  should  be  placed  in  tanks,  or  troughs,  or  other  receptacles 
made  of  any  suitable  material,  as  wood  (if  of  wood,  preferably  lined  with  stoneware 
slabs),  and  thoroughly  drenched,  soaked,  or  impregnated  with  my  composition,  which 
is,  after  a  time,  to  be  drawn  off  and  washed  out,  or  displaced  with  water,  in  order  that 
the  contained  precious  metal  may  be  separated  by  subsequent  operations. 

The  composition  may  be  used  hot  or  cold.  The  effect  of  heat  is  to  hasten  the  chem- 
ical and  solvent  action. 

What  I  claim,  and  desire  to  secure  by  Letters  Patent  of  the  United  States,  is— 

The  before-described  composition  of  matter — to  be  used  for  extracting  gold  and  silver 
from  minerals,  tailings,  and  other  matters  containing  one  or  both  of  these  metals — con- 
sisting of  water,  one  or  more  soluble  ferricyanides,  and  one  or  more  soluble  cyanides, 
prepared  and  combined  as  herein  stated. 

EDWARD  D.  KENDALL. 

Witnesses : 

Edward  M.  McCook. 
•  S.  J.  Stokes. 


118  THE    CYANIDE    PROCESS 

[Second  Edition.] 

No.  3,024.  A.  D.  1892. 

Date  of  Application,  16th  Feb.,  1892. 

Complete  Specification  Left  16th  Nov..  1892— Accepted  16th  Feb.,  1893. 

PROVISIONAL  SPECIFICATION. 

IMPROVEMENTS  IN  PRECIPITATING  AND  COLLECTING  METALS  FROM  SOLUTIONS 
CONTAINING  THEM. 


A  communication  by  Bernard  Charles  Molloy,  Member  of  Parliament,  Barrister  at  Law, 
of  the  Middle  Temple,  London,  temporarilj'^  residing  in  Jolaannesburg,  South  Afri- 
can Republic. 

I,  Alfred  George  Brookes,  of  55  and  56  Chancery  Lane,  in  the  county  of  London,  Char- 
tered Patent  Agent,  do  hereby  declare  the  nature  of  this  invention  to  be  as  follows : 

This  invention  consists  in  a  new  method  of  precipitating  and  collecting  gold  and  other 
metals  from  solutions  containing  these  metals,  such  as  bromide,  chloride,  and  cyanide 
solutions. 

In  some  cases  these  solutions  are  acid,  but  under  the  action  of  this  process  these  solu- 
tions are  rendered  neutral  and  alltaline,  so  that  the  solutions  are,  or  become,  alkaline 
solutions  of  the  metals  which  are  soluble  in  alkaline  solution. 

The  application  of  this  process  may  be  carried  out  in  apparatus  of  many  forms  of  con- 
struction and  under  many  and  differing  conditions,  depending  on  the  character  of  the 
work  required  to  be  done. 

The  following  example  will,  however,  explain  the  nature  of  the  process,  and  how  it 
may  be  carried  out: 

Take  a  tray  or  tank  constructed  of  wood,  cement,  or  other  suitable  material  and  of  a 
size  as  may  be  necessary. 

Cover,  or  partially  cover,  the  bottom  of  the  tank  with  mercury.  On  this  mercury  will 
rest  the  solution  from  which  the  metals  are  to  be  precipitated.  This  mercury  is  then 
charged  electrolytically  with  ammonium,  sodium,  potassium,  or  other  alkaline  metal, 
which  is  then  amalgamated  by  the  mercury.  These  alkaline  metals,  or  the  amalgams  of 
these  metals,  when  they  come  to  the  surface  of  the  mercury  and  in  contact  with  the 
water  of  the  solution,  decompose  the  water,  the  alkaline  metal  combining  with  the  oxy- 
gen of  the  water  to  form  an  alkaline  oxide,  and  so  rendering  the  solution  alkaline  if  not 
previously  so,  and  the  hydrogen  of  the  decomposed  water  is  at  the  same  time  evolved 
in  a  nascent  state  from  the  surface  of  the  mercury  in  contact  with  and  against  the  solu- 
tion from  which  the  metal  in  solution  (say  the  gold)  is  to  be  precipitated  and  collected. 

Under  this  action  the  metals  in  solution  (such  as  gold)  will  be  precipitated  and  ab- 
sorbed by  the  merctiry,  from  which  it  can  be  released  in  the  ordinary  manner  by  the 
action  of  heat. 

In  the  above-described  case  the  charging  of  the  mercury  with  the  alkaline  metal  has 
been  effected  electrolytically  by  the  electrolysis  of  say  an  alkaline  salt  of  the  alkaline 
metal  used  in  a  porous  vessel  in  contact  with  a  mercury  cathode  or  other  convenient 
method. 

Another  though  much  less  advantageous  method  is  the  mechanical  addition  to  the 
mercury,  of  potassium  or  other  alkaline  metal  or  amalgam  of  the  same,  when  the  nascent 
hydrogen  with  an  equivalent  of  the  alkaline  oxide  will  be  produced. 

These  are  some  methods  by  which  the  process  may  be  carried  out,  but  there  are  others, 
as  is  evident,  which  may  be  employed. 

In  carrying  out  this  process  a  solution  of  bromine,  chlorine,  or  cyanogen  may  be  used 
to  dissolve  the  gold  and  other  metals  from  their  compounds,  and  then  the  process  here 
described  may  be  used  to  precipitate  and  collect  the  metals. 

It  is  evident  that  generation  of  nascent  hydrogen  in  contact  with  an  alkaline  solution 
of  metals,  soluble  in  such  solution,  may  be  obtained  by  other  means,  though  not  detailed 
here. 

Dated  the  16th  day  of  February,  1892. 

WM.  BROOKES  &  SON, 
55  and  56  Chancery  Lane,  London,  Agents  for  the  Applicant. 


PATENT-SPECIFICATIONS.  119 

COMPLETE  SPECIFICATION. 

IMPROVEMENTS  IN  PRECIPITATING  AND  COLLECTING  METALS  FROM  SOLUTIONS  CON- 
TAINING THEM. 

A  communication  by  Bernard  Charles  Molloj'-,  Member  of  Parliament,  Barrister  at  Law, 
of  the  Middle  Temple,  London,  temporarily  residing  in  Johannesburg,  South  Afri- 
can Republic. 

I,  Alfred  George  Brookes,  of  55  and  56  Chancery  Lane,  in  the  county  of  London, 
Chartered  Patent  Agent,  do  hereby  declare  the  nature  of  this  invention  and  in  what 
manner  the  same  is  to  be  performed,  to  be  particularly  described  and  ascertained  in  and 
by  the  following  statement : 

This  invention  consists  in  a  new  method  of  precipitating  and  collecting  the  gold  and 
other  metals  from  the  solutions  containing  these  metals,  such  as  bromide,  chloride,  and 
cyanide  solutions,  when  such  are  employed  for  dissolving  out  the  precious  metals  from 
compounds  containing  the  same. 

In  some  cases  these  solutions  are  acid,  but  under  the  action  of  this  process  these  solu- 
tions are  rendered  neutral  and  alkaline,  so  that  the  solutions  are,  or  become,  alkaline 
solutions  of  the  metals,  which  are  soluble'in  alkaline  solutions. 

The  application  of  this  process  may  be  carried  out  in  apparatus  of  many  forms  of  con- 
struction, and  under  many  and  differing  conditions,  depending  on  the  character  of  the 
work  required  to  be  done. 

The  following  example  of  the  treatment  of  a  gold-bearing  compound  will,  however 
explain  the  nature  of  the  process,  and  how  it  may  be  carried  out: 

The  crushed  ore  is  treated,  say,  with  a  solution  of  cyanide  of  potassium,  the  quantity 
and  saturation  being  in  proportion  to  the  work  to  be  done.  When  the  solvent  solution 
is  sufficiently  charged,  then  the  precipitation  of  the  gold,  the  regeneration  of  this  solvent, 
and  the  collection  of  the  gold,  is  effected  as  follows: 

Take  a  tray,  or  tank,  constructed  of  wood,  cement,  or  other  suitable  material,  and  of  a 
size  as  may  be  necessary.  Cover,  or  partially  cover,  the  bottom  of  the  tank  with  mer- 
cury. 

On  this  mercury  will  rest,  or  pass  over,  the  solution  from  which  the  metals  are  to  be 
precipitated.  This  mercury  is  then  charged  electrolytically  with  ammonium,  sodium, 
potassium,  or  other  alkaline  metal.  These  alkaline  metals,  when  they  come  to  the  sur- 
face of  the  mercury  and  in  contact  with  the  water  of  the  solution  (now  containing  gold) 
decompose  the  water,  the  alkaline  metal  combining  with  the  oxygen  of  the  decompose(i 
water  to  form  an  alkaline  oxide,  rendering  the  solution  alkaline,  if  not  previously  so, 
and  the  hydrogen  of  the  decomposed  water  is  at  the  same  time  evolved  in  a  nascent 
state  from  the  surface  of  the  mercury  in  contact  with  and  against  the  solution  from 
which  the  metal  in  solution  (say  the  gold)  is  to  be  precipitated  and  collected.  While 
the  current  continues  to  pass,  the  required  nascent  hydrogen  and  oxide  will  be  produced 
and  act  on  the  solution  containing  the  gold. 

Under  this  action  the  metals  in  solution  such  as  gold  will  be  precipitated  and  ab- 
sorbed by  the  mercury,  from  which  it  can  be  released  in  the  ordinary  manner  by  the 
action  of  heat. 

In  the  above-described  case,  the  charging  of  the  mercury  with  the  alkaline  metal  has 
been  effected  electrolytically  by  the  electrolysis  of,  say,  an  alkaline  salt  of  the  alkaline 
metal  used  in  a  porous  vessel  in  contact  with  the  mercury  cathode  or  other  convenient 
method. 

Another  though  less  advantageous  method  is  the  mechanical  addition  to  the  mercury 
of  potassium,  or  other  alkaline  metal,  or  amalgam  of  the  same,  when  the  nascent  hydro- 
gen, with  an  equivalent  of  the  alkaline  oxide,  will  be  produced. 

These  are  some  methods  by  which  the  process  maybe  carried  out,  but  there  are  others 
as  is  evident,  which  may  be  employed  instead.  ' 

The  action  may  be  concisely  aescribed  as  follows : 

The  precious  metal  is  dissolved  out  say  by  a  solution  of  potassium  cyanide.  The  solu- 
tion is  then  brought  into  contact  with  mercury,  charged,  as  described,  with  potassium. 
The  potassium  on  coming  into  contact  with  the  water  of  the  solution  decomposes  it 
with  the  evolution  of  nascent  hydrogen  and  the  formation  of  the  oxide  of  the  alkaline 
metal.  The  hydrogen  decomposes  the  solution  of  the  new  cyanide  of  gold— and  sets  the 
gold  free,  which  is  precipitated  upon  and  collected  by  the  mercury. 

The  metal  of  the  alkaline  oxide  reacts  upon  the  cyanogen  compound,  and  so  reforms 
or  reproduces  the  cyanide  of  potassium.  The  original  solution  (of  cyanide  of  potas- 
sium) is  thus  regenerated,  and  is  then  ready  for  re-use,  thus  effecting  a  great  economv. 

The  following  equations  roughly  represent  the  various  reactions  when  cvanogen  "is 
the  solvent : 

H,0  +  0  -f4  KCN  -1-2  Au  =  2  (KAu(CN),)  -f-  2  KOH  2  (KAu(CN),)  -f  2  H  = 
2  KCN  -f  2  CNH  -}-  2  Au  2  CNH  -f-  2  KOH  =  2  KCN  -f-  2  HjO 

In  carrying  out  this  process  a  suitable  solution  of  a  solvent  for  gold,  such  as  bromine 
or  chlorine,  or  cyanogen,  or  their  compounds,  mav  be  used  to  dissolve  out  the  gold  and! 
other  metals  from  their  ores  or  compounds,  and  then  the  process  more  particularly 
described  for  precipitating  the  metals  in  such  solution,  and  in  some  cases  regenerating 
the  solvent  solutions  and  obtaining  the  metals. 


120  THE   CYANIDE    PROCESS. 

It  is  evident  that  generation  of  nascent  hydrogen  in  contact  with  an  alkaline  solution 
from  which  metals  soluble  in  such  solution  are  to  be  precipitated,  may  be  obtained 
without  the  employment  of  a  cathode  of  mercury,  and  using  instead  thereof  another 
known  cathode. 

Although  I  have  hereinbefore  indicated  some  methods  by  which  it  may  be  worked, 
variations  in  detail  may  be  effected  without  departing  from  the  essential  features  of  my 
invention. 

Having  now  particularly  described  and  ascertained  the  nature  of  my  said  invention, 
and  in  wnat  manner  the  same  is  to  be  performed,  I  declare  that  what  I  claim  is — 

1.  The  method  of  obtaining  gold  and  other  metals  from  solutions  which  have  been 
employed  in  dissolving  out  such  precious  metals  from  ores,  or  compounds,  containing 
the  same,  substantially  in  the  manner  and  for  the  purpose  hereinbefore  set  forth. 

2.  The  described  method  of  precipitating  and  collecting  gold  and  other  metals  from 
solutions,  such  as  referred  to,  containing  them,  by  the  action  of  the  alkaline  metals,  in 
the  manner  hereinbefore  set  forth. 

3.  The  extraction  of  gold  or  other  metals  from  ores,  or  other  compounds,  by  solutions 
of  cyanogen,  or  its  compounds,  the  precipitation  of  gold  or  other  metals  from  such  solu- 
tions, the  regeneration  of  such  solutions,  and  the  collection  of  the  gold  or  other  metal, 
all  substantially  as  and  for  the  purpose  set  forth. 

4.  The  described  method  of  precipitating  gold  and  other  metals  from  alkaline  solutions, 
such  as  indicated,  containing  them,  by  the  action  of  nascent  hydrogen,  in  the  manner 
hereinbefore  set  forth. 

5.  The  precipitation  of  gold,  and  other  precious  metals  from  solutions,  such  as  indi- 
cated, containing  them,  by  means  of  the  alkaline  metals,  or  amalgams  of  the  same, 
obtained  electrolytically,  substantially  as  and  for  the  purpose  set  forth. 

6.  The  separation  and  collection  of  gold  or  other  precious  metals  from  their  ores  or 
compounds  by  means  of  a  suitable  solvent  for  said  metals,  an  electrolyte  of  the  alka- 
line metals,  a  current  of  electricity,  a  mercury  cathode,  all  substantially  as  set  forth. 

7.  The  employment  of  bromine,  chlorine,  iodine,  and  cyanogen,  or  their  compounds, 
as  solvents  for  gold  or  other  metals,  in  combination  with  the  above-described  process 
for  effecting  the  precipitation  and  collection  of  the  gold  and  other  metals  in  solution 
therein,  substantially  as  set  forth. 

Dated  the  16th  day  of  November,  1892. 

WM.  BROOKES  &  SON, 
55  and  56  Chancery  Lane,  London,  Agents  for  the  Applicant. 


PATENT-SPECIFICATIONS.  121 

[Second  Edition.] 

No.  12,641.  A.  D.  1892. 

Date  of  Application,  8th  July,  1892. 
Complete  Specification  Left  10th  April,  1893— Accepted  8th  July,  1893. 


PROVISIONAL  SPECIFICATION. 

IMPROVEMENTS  IN  THE  EXTRACTION  OF  GOLD  AND  SILVER  FROM  ORES  OR  COM- 
POUNDS CONTAINING  THE  SAME,  AND  IN  APPARATUS  APPLICABLE  FOR  USE  IN 
THE  TREATMENT  OF  SUCH  MATERIALS  BY  MEANS  OF  SOLVENTS. 

I,  John  Cuninghame  Montgomerie,  of  the  "Water  of  Ayr"  and  "Tarn  O'Shanter" 
Hone  Works,  Dalmore,  Stair,  in  the  county  of  Ayr,  manufacturer,  do  hereby  declare  the 
nature  of  this  invention  to  be  as  follows  : 

This  invention  relates  to  the  treatment  of  auriferous  and  argentiferous  ores  or  com- 
pounds, for  the  purpose  of  separating  and  collecting  the  gold  and  silver  contained 
therein,  by  means  of  solvent  agents — as,  for  example,  cyanide  of  potassium— and  to 
apparatus  applicable  for  use  in  processes  of  this  description. 

According  to  the  method  usually  employed  in  the  recovery  of  gold  and  silver  by 
means  of  cyanide  of  potassium,  the  ore  or  other  material  having  been  reduced  to  a 
finely-triturated  state  is  placed,  along  with  the  solvent,  in  a  barrel  or  other  vessel  and 
is  there  subjected  to  agitation.  After  the  lapse  of  a  few  hours  the  conte'uts  of  the  barrel 
are  removed  to  a  filter,  where  the  liquid  portion  of  the  charge  (containing  the  precious 
metals  in  solution)  is  separated  from  the  ore.  The  latter  is  further  washed  for  the 
removal  of  any  gold  or  silver  remaining  (in  solution)  therewith.  The  cyanide  solution 
of  gold  and  silver  (as  also  the  wash-water)  is  then  treated  for  the  recovery  of  the  pre- 
cious metals  by  precipitation. 

When  a  cyanide  solvent  is  employed  as  hereinbefore  described,  the  proportion  of 
cjranide  is  necessarily  considerably  in  excess  of  that  required  for  chemical  combination 
with  the  gold  and  silver  present  in  the  ore.  This  excess  remains  with  the  liquor  after 
the  precious  metals  have  been  precipitated  therefrom,  and  is  either  run  to  waste  or  is 
subjected  to  a  separate  process  for  the  recovery  of  the  cyanide. 

My  improvement  in  the  process  of  extraction  by  the  method  hereinbefore  referred  to 
consists  in  applying  the  cyanide  solution  of  gold  and  silver,  after  having  been  separated 
from  the  ore  by  filtration,  to  a  subsequent  charge  or  to  subsequent  charges  of  fresh  ore 
prior  to  treating  the  solution  for  the  separation  of  the  precious  metals  by  precipitation, 
care  being  taken  that  the  original  quantity  of  water  is  made  good.  With  this  object 
the  requisite  quantity  of  water  is  preferably  added  as  soon  as  the  surface  of  the  ore 
contained  in  the  filter  presents  a  dry  appearance,  the  added  water  displacing  the  liquid 
remaining  in  the  ore  and  permitting  the  same  (which  is  highly  charged  with  the  sol- 
vent and  with  the  precious  metals  in  solution)  to  be  discharged.  The  solution  is  then 
tested  for  cyanide  of  potassium  (or  such  other  solvent  agent  as  may  be  employed),  and 
the  deficiency  supplied  by  the  addition  of  a  suitable  quantity  of  cyanide  of  potassium 
(or  other  solvent  agent),  thereby  restoring  the  solvent  solution  to  its  original  strength 
before  adding  the  same  to  the  fresh  charge  of  ore.  Before  being  added  to  the  fresh 
charge  of  ore,  the  solution  is  made  slightly  alkaline  by  the  addition  of  an  alkali,  prefer- 
ably caustic  soda. 

Where  cyanide  is  employed,  it  is  necessary  for  the  ore  to  be  thoroughly  neutralized 
before  treatment;  and  in  some  cases  it  is  advantageous  to  have  it  slightly  alkaline, 
especially  where  oxygen  is  used  under  pressure.  The  tailings  are  then  further  washed' 
to  remove  the  last  trace  of  gold  and  silver  remaining  in  solution,  and  the  resultant 
wash-water  is  treated  in  the  usual  way  for  the  recovery  of  the  precious  metals  contained 
therein. 

By  this  mode  of  procedure  considerable  economy  is  effected,  both  in  the  quantity  of 
cyanide  or  other  solvent  used  and  in  the  cost  of  working,  the  quantity  of  liquid  sub- 
jected to  treatment  for  the  recovery  of  the  gold  and  silver  by  precipitation  being  at  the 
same  time  greatly  reduced. 

My  invention  relates  secondly  to  the  construction  of  the  barrel  or  other  vessel  in 
which  the  ore  is  subjected  to  the  action  of  the  solvent. 

If  this  barrel  or  vessel  be  formed  of  metal,  its  internal  surface  is  rapidly  acted  upon 
by  cyanide  of  potassium  or  other  solvent  of  the  precious  metals  ;  and  if  a  lining  of  wood 
or  similar  material  be  employed,  the  latter  is  incapable  of  withstanding  the  chemical 
action  of  the  solvent  and  the  abrasive  action  of  the  ore  for  any  length  of  time. 

With  a  view  to  overcoming  these  difficulties,  I  line  the  barrel  or  vessel  with  tiles  or 
segments  composed  of  glass  or  glazed  porcelain  or  similar  solvent-  and  acid-resisting 
material,  the  same  being  set  in  cement  adapted  to  withstand  the  chemical  action  of  the 
cyanide  or  other  solvent  employed. 


122  THE   CYANIDE   PROCESS, 

My  invention  relates  thirdly  to  the  construction  of  the  filter  or  leaching  vat  employed 
for  separating  the  ore  from  the  cyanide  or  other  solution  of  gold  and  silver,  or  from  the 
wash-water. 

A  filter  constructed  according  to  my  improved  method  comprises  an  upper  vessel  for 
the  reception  of  the  mixture  of  ore  and  solvent,  and  a  lower  vessel  in  which  the  solution 
is  received  after  passing  through  the  filter-bed.  The  latter  is  formed  of  filter  cloth 
carried  on  wire  gauze  coated  with  an  acid-proof  enamel  and  supported  on  wooden  laths. 
The  upper  vessel  is  attached  to  the  lower  vessel  by  means  of  bolts,  and  is  so  arranged 
that  the  bottom  edge  of  the  former  rests  upon  the  periphery  of  the  filter  cloth  and  grips 
the  same  in  a  recess  formed  in  the  upper  edge  of  the  lower  vessel,  thereby  securing  a 
water-tight  joint  between  the  two  vessels  and  at  the  same  time  holding  the  filter  cloth 
securely  in  position. 

The  filter  or  leaching  vat  may  be  lined  with  segments  or  tiles  in  the  manner  herein 
before  described  with  reference  to  the  barrel  or  other  vessel  in  which  the  ore  is  subjected 
to  the  action  of  the  solvent. 

Dated  the  6th  day  of  July,  1892. 

G.  G.  M.  HARDINGHAM, 
191  Fleet  Street,  London,  E.G.,  Chartered  Patent  Agent. 


COMPLETE  SPECIFICATION. 

IMPROVEMENTS  IN  THE  EXTRACTION  OF  GOLD  AND  SILVER  FROM  ORES  OR  COM- 
POUNDS CONTAINING  THE  SAME,  AND  IN  APPARATUS  APPLICABLE  FOR  USE  IN 
THE  TREATMENT  OF  SUCH  MATERIALS  BY  MEANS  OF  SOLVENTS. 

I,  John  Cuninghame  Montgomerie,  of  the  "Water  of  Ayr"  and  "Tarn  O'Shanter" 
Hone  Works,  Dalmore,  Stair,  in  the  county  of  Ayr,  Scotland,  manufacturer,  do  hereby 
declare  the  nature  of  this  invention,  and  in  what  manner  the  same  is  to  be  performed,  to 
be  particularly  described  and  ascertained  in  and  by  the  following  statement: 

This  invention  relates  to  the  treatment  of  auriferous  and  argentiferous  ores  or  com- 
pounds, for  the  purpose  of  separating  and  collecting  the  gold  and  silver  contained 
therein,  by  means  of  solvent  agents— as,  for  example,  cyanide  of  potassium — and  to 
apparatus  applicable  for  use  in  processes  of  this  description. 

According  to  a  method  commonly  employed  in  the  recovery  of  gold  and  silver  by 
means  of  cyanide  of  potassium,  the  ore  or  other  material  having  been  reduced  to  a 
finely-triturated  state  is  placed,  along  with  the  solvent,  in  a  barrel  or  other  vessel,  and 
is  there  subjected  to  agitation.  After  the  lapse  of  a  few  hours,  the  contents  of  the  barrel 
are  removed  to  a  filter,  where  the  liquid  portion  of  the  charge  (containing  the  precious 
metals  in  solution)  is  separated  from  the  ore.  The  latter  is  further  washed  for  the 
removal  of  any  gold  or  silver  remaining  (in  solution)  therewith.  The  cyanide  solution 
of  gold  and  silver,  as  also  the  wash-water,  is  then  treated  for  the  recovery  of  the  precious 
metals  by  precipitation  in  a  zinc  filter  or  percolator. 

When  a  cyanide  solvent  is  employed  as  hereinbefore  described,  a  certain  portion 
thereof  is  taken  up  by  base  metals  and  other  impurities  invariably  present  in  greater  or 
less  proportions  in  the  ore.  The  solvent  is  also  contaminated  *by  the  zinc  dissolved 
whilst  the  mixture  of  ore  and  solvent  is  under  treatment  in  the  zinc  percolator ;  both  of 
these  causes  resulting  in  a  considerable  waste  of  the  cyanide,  and  in  its  contamination 
with  deleterious  matter. 

My  improvement  in  the  process  of  extraction  by  means  of  the  kind  hereinbefore 
referred  to,  consists  in  adding  sodium  oxide  (caustic  soda),  or  other  suitable  oxide  of  the 
alkalies,  to  the  cyanide  solution  before  (or  whilst)  mixing  the  same  with  the  ore, 
thereupon  agitating  or  otherwise  treating  the  resultant  mass  for  the  time  requisite  for 
enabling  the  gold  and  silver  to  be  dissolved  by  such  a  solution,  then  discharging  the 
same  into  a  filter  and  drawing  off  the  original  quantity  of  water  employed,  the  same 
being  highly  charged  with  the  unconsumed  cyanide  and  sodium  oxide,  and  with  the 
preciou%  metals  in  solution. 

By  the  employment  of  sodium  oxide  in  the  manner  hereinbefore  described,  particu- 
larly where  the  alkali  is  in  excess,  I  have  found  that  the  proportion  of  cyanide  or  other 
solvent  may  be  considerably  reduced  and  an  important  economy  in  the  cost  of  working 
effected. 

In  carrying  out  this  stage  of  the  process,  a  sufficient  quantity  of  water  is  added  to  the 
surface  of  the  ore  in  the  filter  as  soon  as  it  becomes  dry,  the  added  water  displacing  the 
liquid  remaining  in  the  ore  and  permitting  the  latter  to  be  discharged.  The  liquid 
obtained  is  then  tested  for  cyanide  of  potassium  and  sodium  oxide,  and  the  deficiency 
supplied  by  the  addition  of  the  necessary  quantity  of  these  agents  so  as  to  restore  the 
son'ent  solution  to  its  original  character  and  strength.  This  solution  is  now  applied  to 
a  fresh  charge  of  ore,  and  the  same  operation  is  repeated  with  successive  charges  till  it 
is  found  necessary  to  discharge  the  solution  with  a  view  to  precipitating  the  gold  and 
silver  in  the  usual  manner.  Experiment  alone  can  determine  the  quantity  of  solvent 
and  of  sodium  oxide  appropriate,  and  the  period  of  time  requisite  to  insure  the  greatest 
extraction  of  the  precious  metals  with  the  least  consumption  of  the  solvent,  as  these 
will  vary  according  to  the  nature  of  the  ore  operated  upon.    (It  may  be  mentioned  by 


PATENT-SPECIFICATIONS. 


123 


AD.   1892.  JuLT  8.  N"    12,641. 
MONTGOMERIE'S  Complbte  Specification. 


124  THE    CYANIDE    PROCESS. 

way  of  illustration  that  for  an  ore  containing  about  4  ozs.  of  gold  and  12  ozs.  of  silver 
per  ton,  12  lbs.  of  cyanide  of  potassium  and  3  lbs.  of  sodium  oxide  would  be  suitable.) 
The  tailings  are  then  further  washed  to  remove  the  last  trace  of  gold  and  silver  remain- 
ing in  solution,  and  the  resultant  wash-water  is  treated  in  the  usual  way  for  the  recovery 
of  the  precious  metals  contained  therein. 

By  this  mode  of  procedure,  the  quantity  of  liquid  subjected  to  treatment  for  the 
recovery  of  the  gold  and  silver  by  precipitation  is  greatly  reduced. 

My  invention  relates  secondly  to  the  construction  of  the  barrel  or  other  vessel  in 
which  the  ore  is  subjected  to  the  action  of  the  solvent. 

If  this  barrel  or  vessel  be  formed  of  metal,  its  internal  surface  is  rapidly  acted  upon 
by  cyanide  of  potassium  or  other  solvent  of  the  precious  metals;  and  if  a  lining  of  wood 
or  similar  material  be  employed,  the  latter  is  incapable  of  withstanding  the  chemical 
action  of  the  solvent  and  the  abrasive  action  of  the  ore  for  any  length  of  time. 

With  a  view  to  overcoming  these  difficulties,  I  line  the  barrel  or  vessel  with  tiles  or 
segments  composed  of  glass  or  glazed  porcelain,  or  similar  solvent-  and  acid-resisting 
material,  the  same  being  set  in  cement  adapted  to  withstand  the  chemical  action  of  the 
cyanide  or  other  solvent  employed. 

My  invention  relates  thirdly  to  the  construction  of  the  filter  or  leaching  vat  employed 
for  separating  the  ore  from  the  cyanide  or  other  solution  of  gold  and  silver,  or  from  the 
wash-water. 

Apparatus  constrticted  according  to  my  invention  is  illustrated  in  the  accompanying 
drawings,  w^hereof  Fig.  1  is  a  vertical  section,  and  Fig.  2  a  plan.  The  apparatus  com- 
prises an  upper  vessel  A  for  the  reception  of  the  mixture  of  ore  and  solvent,  and  a  lower 
vessel  B  in  which  the  solution  is  received  after  passing  through  the  filter-bed.  The 
latter  is  formed  of  filter-cloth  C  carried  on  wire  gauze  D  coated  with  an  acid-proof  enamel 
and  supported  on  wooden  laths  E  on  the  top  of  the  vessel  B.  The  vessel  A  is  attached 
to  the  vessel  B  by  means  of  bolts  F  and  nuts  Fi,  and  is  so  arranged  that  its  bottom  edge 
rests  upon  the  circular  margin  of  the  filter-cloth  0,  which  it  presses  against  the  bottom 
of  a  recess  or  socket  formed  in  the  upper  edge  of  the  vessel  B,  thereby  securing  a  water- 
tight joint  between  the  two  vessels  and  at  the  same  time  holding  the  filter-cloth 
securely  in  position.  G  is  a  draw-off  cock;  H  being  the  exhaust  cock.  The  vessels  A 
and  B  are  lined  with  segments  or  tiles  K,  composed  of  glass,  glazed  porcelain,  or  similar 
solvent-  and  acid-resisting  material,  set  in  cement  adapted  to  withstand  the  chemical 
action  of  the  cyanide  or  other  solvent  employed.  When  a  barrel  is  used,  it  may  be  lined 
with  segments  or  tiles  set  in  a  similar  manner. 

Having  now  particularly  described  and  ascertained  the  nature  of  this  invention,  and 
in  what  manner  the  same'is  to  be  performed,  I  claim — 

1.  The  improved  process  of  extracting  gold  and  silver  from  ores  or  compounds  con- 
taining the  same,  substantially  as  herein  described;  the  same  consisting  in  mixing  the 
ore  with  a  solution  of  cj'anide  of  potassium  or  other  cyanide  solvent  rendered  alkaline 
by  the  addition  of  sodium  oxide  or  an  eqi^ivalent  alkaline  oxide,  filtering  or  otherwise 
separating  the  liquid  (containing  the  gold  and  silver  in  solution)  from  the  ore,  and 
treating  the  former,  by  precipitation  or  other  known  mode,  for  the  recovery  of  the 
precious  metals. 

2.  In  the  extraction  of  the  precious  metals  by  a  solvent  process  of  the  general  char- 
acter herein  referred  to,  applymg  the  solvent  solution,  after  separation  from  the  first 
charge  of  ore,  to  a  subsequent  charge  or  successively  to  subsequent  charges  of  fresh  ore, 
the  solution  being  fortified  at  each  operation  by  the  addition  of  a  suitable  quantity  of 
the  chemical  agents  employed,  and  ultimately  treating  the  liquid  (consisting  of  a  more 
or  less  saturated  solution  of  gold  and  silver)  by  any  known  means  for  the  separation 
and  recovery  of  the  precious  metals. 

3.  In  the  process  of  extracting  gold  and  silver  by  means  of  cyanide  of  potassium  or 
other  cyanide  solvent,  the  addition  of  sodium  oxide  or  other  suitable  alkaline  oxide  to 
the  solvent,  either  prior  to  or  during  its  admixture  with  the  ore,  for  the  purpose  of 
economizing  the  solvent  and  expediting  its  action. 

4.  In  the  extraction  of  the  precious  metals  by  a  solvent  process  of  the  general  char- 
acter herein  referred  to,  discharging  the  solvent  remaining  with  the  ore  after  filtration 
by  adding  water  to  the  surface  of  the  ore  and  thereby  displacing  the  solvent  containing 
the  precious  metals  in  solution,  substantially  as  herein  described. 

5.  In  apparatus  adapted  for  use  in  the  treatment  of  ores  or  compounds  containing 
gold  or  silver,  a  barrel,  filter,  or  leaching  vessel  such  as  A  or  B  lined  with  tiles  K  set  in 
an  acid-  or  solvent-resisting  cement,  substantially  as  herein  described. 

6.  The  herein  described  apparatus  for  use  in  the  treatment  of  ores  or  compounds  con- 
taining gold  and  silver  by  means  of  solvents,  the  same  comprising  an  upper  vessel  A  for 
the  reception  of  the  ore  and  solvent,  a  lower  vessel  B  in  wnich  tne  solution  is  received, 
a  filter  cloth  C  held  between  the  lower  part  of  the  vessel  A  and  a  socket  in  the  upper 
part  of  the  vessel  B,  wire  gauze  D  on  which  the  filter  cloth  lies,  and  bars  E  for  support- 
ing the  wire  gauze. 

7.  The  herein  described  apparatus  for  use  in  the  treatment  of  ores  or  compounds  con- 
taining gold  and  silver  by  means  of  solvents,  the  same  comprising  an  upper  vessel  A 
lined  with  tiles  K,  a  lower  vessel  B  also  lined  with  tiles  K,  a  filter  cloth  C  held  between 
the  vessels  A  and  B,  wire  gauze  D  under  the  filter  cloth,  bars  E  for  supporting  the  wire 
gauze,  a  draw-off  cock  G,  and  an  exhaust  cock  H. 

Dated  the  8th  day  of  April,  1893. 

G.  G.  M.  HARDINGHAM, 
191  Fleet  Street,  London,  E.G.,  Chartered  Patent  Agent. 


PATENT-SPECIFICATIONS.  125 

UNITED  STATES  PATENT  OFFICE. 


ALEXIS   JANIN  and   CHARLES   W.   MERRILL,   of   San   Francisco,  California. 
PKOCESS  OF  LEACHING  ORES  WITH  SOLUTIONS  OF  ALKALINE  CYANIDES. 


Specification  forming  part  of  Letters  Patent  No.  515,148,  dated  February  20,  1894. 
(Application  filed  June  12, 1893.    Series  No.  477,.338.    No  specimens.) 

To  all  whom  it  may  concern: 

Be  it  known  tliat  we,  Alexis  Janin  and  Charles  W.  Merrill,  citizens  of  the  United 
States  residing  in  the  city  and  county  of  San  Francisco,  State  of  California,  have  invented 
an  Improvement  in  Processes  of  Leaching  Ores  with  Solutions  of  Alkaline  Cyanides;  and 
we  hereby  declare  the  following  to  be  a  full,  clear,  and  exact  description  of  the  same: 

Our  invention  relates  to  an  improvement  in  the  art  of  leaching  ores  with  solutions  of 
alkaline  cyanides,  and  consists  in,  first,  precipitating  and  separating,  in  the  form  of  silver 
sulphide,  by  means  of  an  alkaline  sulphide  or  of  sulphuretted  hydrogen  gas,  all  or  the 
greater  portion  of  the  silver  dissolved  from  the  ore  by  such  solutions,  and  then  precipi- 
tating in  the  metallic  state,  by  means  of  metallic  zinc,  the  gold  contained  in  the  same 
solution,  together  with  any  silver  which  has  escaped  precipitation  as  a  sulphide. 

In  the  usual  method  of  leaching  ores  with  a  solution  of  potassium  cyanide,  the  gold 
and  silver  extracted  are  both  precipitated  from  the  solution  in  the  metallic  state,  with 
metallic  zinc.  When  much  silver  is  present,  this  method  involves  a  large  consumption 
of  zinc  and  consequent  contamination  of  the  cyanide  solution  by  the  zinc  dissolvec^  and 
unless  the  contact  between  the  zinc  and  the  silver- bearing  solution  be  greatly  prolonged, 
the  precipitation  of  the  silver  is  imperfect.  Furthermore,  the  potassium  cyanide  which 
combines  with  the  zinc  dissolved  is  practically  lost.  When  the  silver  is  precipitated 
from  its  solution  in  potassium  cyanide  by  means  of  an  alkaline  sulphide  an  alkaline 
cyanide  is  regenerated,  which  is  again  available  for  leaching.  If  sulphuretted  hydrogen 
gas  be  used  to  precipitate  the  silver  there  is  also  formed  free  hydrocyanic  acid,  but  if  the 
solution  of  potassium  cyanide  contains  free  alkali,  or  if  such  be  added  to  the  solution,  no 
free  hydrocyanic  acid  will  escape,  either  because  the  sulphuretted  hydrogen  gas  first  com- 
bines with  the  alkali,  to  form  a  sulphide  which  precipitates  the  silver  in  the  manner 
described,  or  because  any  hydrocyanic  acid  generated  will  also  combine  with  the  free 
alkali  to  form  an  alkaline  cyanide. 

We  have  found  that,  whereas,  silver  is  not  precipitated  at  all,  or  only  very  imperfectly, 
from  strong  solutions  of  potassium  cyanide,  by  means  of  the  agents  hereinafter  men- 
tioned, yet  when  the  silver-bearing  solution  contains  only  about  one  and  one  half  per 
cent,  or  less,  of  pure  potassium  cyanide  (KCN)  or  its  equivalent,  then  the  silver  can  be 
thoroughly  precipitated  by  means  of  the  sulphides  of  sodium,  potassium,  or  ammonium, 
or  by  sulphuretted  hydrogen  gas,  and  the  precipitation  of  the  silver  becomes  more  imper- 
fect as  the  strength  of  the  solution  in  potassium  cyanide  is  increased.  Therefore  when 
leaching  silver-bearing  ores  we  employ  solutions  containing,  at  the  most,  two  per  cent 
of  potassium  cyanide  or  its  equivalent.  As  a  precipitating  agent  we  employ  preferably 
a  solution  of  sodium  sulphide,  approaching,  as  nearly  as  practicable,  to  the  composition 
of  a  monosulphide,  in  order  to  avoid,  as  much  as  possible,  the  separation  of  free  sulphur 
in  precipitating  the  silver. 

In  practice  we  leach  ores  containing  both  gold  and  silver,  with  a  solution  of  potassium 
cyanide  containing  not  more  than  two  percent  of  KCN  or  its  equivalent,  or  as  much 
weaker  as  is  consistent  with  a  thorough  extraction.  The  solution,  after  passing  through 
the  ore,  is  run  into  precipitating  vats,  where  a  solution  of  sodium  sulphide  is  added  in 
suflScient  quantity  to  convert  the  silver  present  into  sulphide  of  silver,  or  in  a  little  less 
than  that  amount,  in  order  to  avoid  the  possibility  of  any  excess  of  the  precipitating 
agent  remaining  in  the  solution  which  might  be  prejudicial  in  its  further  use.  The 
precipitate  of  silver  sulphide  is  allowed  to  settle,  the  supernatant  solution  of  potassium 
cyanide  is  then  drawn  off,  and  the  gold,  together  with  any  silver  remaining  in  solution, 
is  precipitated  by  means  of  metallic  zinc. 

Having  thus  described  our  invention,  what  we  claim  as  new,  and  desire  to  secure  by 
Letters  Patent,  is— 

The  improvement  in  the  art  of  leaching  ores  with  solutions  of  alkaline  cyanides,  which 
consists  in  first  leaching  the  ore  with  such  solutions,  then  adding  to  the  solution  an 
agent  which  will  precipitate  the  silver  present  as  a  sulphide,  and  then  precipitating  the 
gold  in  the  solution  with  metallic  zinc,  substantially  as  herein  described. 

In  witness  whereof  we  have  hereunto  set  our  hands. 

ALEXIS  JANIN. 
CHARLES  W.  MERRILL. 

Witnesses: 

s.  h.  noursk. 
Wm.  F.  Booth. 


126  THE    CYANIDE    PROCESS. 

NEW   ZEALAND  PATENT  OFFICE. 


JOHN  STEWART  MacARTHUR  and  CHARLES  JAMES  ELLIS. 

APPLICATION   FOR   LETTERS   PATENT   FOR   IMPROVEMENTS   IN   EXTRACTING    GOLD 
AND  SILVER  FROM  ORES  AND  THE  LIKE. 


We,  John  Stewart  MacArthur,  Managing  Director  of  the  Cassel  Gold  Extracting  Com- 
pany (Limited),  and  Charles  James  Ellis,  technical  chemist  to  the  said  company,  both 
of  157  West  George  Street,  Glasgow,  in  the  county  of  Lanark,  North  Britain,  do  declare 
the  nature  of  our  invention  for  "Improvements  in  extracting  gold  and  silver  from  ores- 
and  the  like,"  and  in  what  manner  the  same  is  to  be  performed,  to  be  particularly 
described  and  ascertained  in  and  by  the  following  statement: 

Our  said  invention  relates  to  what  is  known  as  the  "MacArthur-Forrest  process"  for 
extracting  gold  and  silver  from  ores  and  the  like  by  means  of  cyanides,  and  has  for  its 
object  to  increase  the  efficiency  and  economy  of  that  process  in  cases  in  which,  from  the 
nature  of  the  ores  treated,  or  other  circumstances,  it  is  found  that  in  the  solution  of  cya- 
nide as  heretofore  used  there  is  formed,  or  becomes  present,  a  sulphide  soluble  therein 
which  retards  and  objectionably  affects  the  action  of  the  cyanide  on  the  precious  metals. 

Our  invention  consists  in  removing  or  rendering  inert  such  sulphide  by  adding  to  the 
solution  of  cyanide,  or  to  the  ore,  or  to  the  mixture  of  ore  and  cyanide  solution,  a 
suitable  salt  or  compound  of  a  metal  which  will  form  with  the  sulphur  of  the  sulphide 
a  sulphide  which  is  practically  insoluble  or  inert  in  the  cyanide  solution,  or  which 
will  materially  diminish  the  objectionable  action. 

In  carrying  out  our  invention,  we  may  use  any  one  or  more  of  various  metallic  salts 
or  compounds,  of  which  the  following  may  be  mentioned,  by  way  of  example,  preference 
being  given  to  them  in  the  order  in  which  they  are  noted,  namely :  Salts  or  compounds 
of  lead,  such  as  plumbates,  carbonate  acetate,  or  sulphate  of  lead;  or  salts  or  compounds 
of  other  metals,  such  as  sulphate  or  chloride  of  manganese,  zincates,  oxide,  or  chloride 
of  mercury,  and  ferric  hydrate,  or  oxide.  The  proportion  to  be  used  in  any  case  will 
depend  on  the  proportion  of  soluble  sulphide  which  has  to  be  dealt  with  in  the  cyanide 
solution  applied  to  the  particular  ore,  and  is  easily  and  most  conveniently  ascertained 
by  trials  of  a  few  samples  in  each  case.  In  the  case  of  some  ores  containing  sulphur,  we 
find  the  addition  of  salts  or  compounds,  as  and  for  the  purpose  hereinbefore  referred  to, 
and  especially  those  of  lead  and  mercurj',  increases  the  percentage  of  precious  metals 
obtained. 

Having  now  particularly  described  our  said  invention,  and  in  what  manner  the  same 
is  to  be  performed,  we  declare  what  we  claim  is — 

1.  In  the  MacArtliur-Forrest  process  for  extracting  gold  and  silver  from  ores  and  the 
like,  the  addition  to  the  cyanide  solution,  or  to  the  ore,  or  to  the  mixture  of  ore  and 
cyanide,  of  salts  or  compounds  of  lead,  substantially  as  and  for  the  purposes  herein- 
before described. 

2.  In  the  MacArthur-Forrest  process  for  extracting  gold  and  silver  from  ores  and  the 
like,  the  addition  to  the  cyanide  solution,  or  to  the  ore,  or  to  the  mixture  of  ore  and 
cyanide,  of  any  one  or  more  of  the  metallic  salts  or  compounds  hereinbefore  indicated, 
and  capable  of  forming  insoluble  sulphides,  as  and  for  the  purposes  hereinbefore 
described. 

Dated  June  29,  1893. 

JOHN  STEWART  MacARTHUR. 
CHARLES  JAMES  ELLIS. 


PATENT-SPECIFICATIONS.  12'i 

NEW  ZEALAND  PATENT  OFFICE. 


CARL  MOLDENHAUER. 

APPLICATION   FOR   LETTERS    PATENT   FOR   IMPROVEMENTS   IN   RECOVERING    GOLD 
AND  OTHER  PRECIOUS  METALS  FROM  THEIR  ORES. 


I,  Carl  Moldenhauer,  of  Frankfort-on-Main,  in  the  Empire  of  Germany,  do  hereby 
declare  that  the  nature  of  my  invention  for  improvements  in  recovering  gold  and  other 
precious  metals  from  their  ores,  and  the  manner  in  which  the  same  i"s  to  be  used,  are 
particularly  described  and  ascertained  in  and  by  the  following  statement: 

This  invention  relates  to  extracting  gold  and  other  precious  metals  from  their  ores  by 
means  of  a  solution  of  cyanide  of  an  alkali  or  an  alkaline  earth,  and  has  for  its  object 
to  render  the  process  more  expeditious  and  considerably  cheaper  than  heretofore. 

The  invention  consists,  firstly,  in  adding  to  the  cyanide  solution  an  artificial  oxidizing 
agent;  and  secondly,  in  precipitating  the  extracted  precious  metal  out  of  its  cyanide 
solution  by  means  of  aluminium  or  alloys  or  amalgam  thereof. 

As  to  the  first  part  of  my  invention,  I  have  found  that  the  dissolving  action  of  the 
cyanide  solution  on  the  precious  metal  is  highly  expedited,  and  much  cvanide  is  saved, 
if  an  artificial  oxidizing  agent  is  added  to  the  said  cyanide  solution.  As  such  an  arti- 
ficial oxidizing  agent,  I  use,  by  preference,  ferricyanide  of  potassium,  or  another  ferri- 
cyanogen  salt  of  an  alkali  or  of  an  alkaline  earth.  In  either  case  the  ferricyanogen  salt 
is  preferably  employed  in  alkaline  solution.  The  result  of  this  addition  of  an  artificial 
oxidizing  agent  is  that  the  dissolving  action  of  the  solvent  is  rendered  more  energetic, 
and  consequently  a  considerably  smaller  quantity  of  the'solvent  is  required.  Thus,  by 
the  addition  of  ferricyanide  of  potassium  or  other  ferricyanogen  salt  in  alkaline  solu- 
tion, as  much  as  80  per  cent  of  the  potassium  may  be  saved.  The  proportions  preferred 
are  from  one  half  to  two  parts  of  ferricyanide  to  one  part  of  cyanide. 

It  may  be  remarked  that  the  ferricyanide  of  potassium  alone  will  not  dissolve  the  gold, 
and  does  not,  therefore,  come  under  the  category  of  the  solvent  heretofore  employed  in" 
processes  of  extraction.  It  does  not,  therefore,  render  unnecessary  the  employm'ent  of 
the  simple  cyanide  as  a  solvent,  but  only  reduces  the  amount  required,  owing  to  the 
capacity  of  the  ferricyanide  to  act  as  an  oxidizing  agent;  consequentiv  the  cyanogen  of 
the  ferricyanide  is  not  used  to  form  the  gold  cyanide  compound.  I'may  also  employ 
permanganate  of  potash  as  the  oxidizing  agent  instead  of  the  ferricyanide.  The  said 
permanganate  of  potash  is  also  added  in  solution  and  in  the  same  proportions  as  before 
namely,  from  one  half  to  two  parts  of  permanganate  to  one  part  of  cyanide. 

In  lieu  of  permanganate  of  potash,  any  other  suitable  oxidizing  agent  can  be  used  in 
carrying  out  my  invention  in  practice,  the  invention  not  being  restricted  to  the  use  of 
any  special  oxidizing  agent,  but  includes  the  use  of  an  agent  that  exerts  an  oxidizing 
action  in  the  cyanide  solution.  The  process  can  be  carried  out  in  a  ball-mill  lined  with 
porcelain,  wood,  or  other  substance  unattackable  by  the  chemicals  employed. 

I  may  also  use  the  cyanide  solution  and  the  oxidizing  agent  in  combination  with  a 
preliminary  treatment  of  the  ore  with  any  acid  or  salt  that  renders  the  precious  metal 
better  adapted  to  the  subsequent  treatment  of  the  cyanide  solution. 

The  second  part  of  the  process  consists  in  precipitating  the  dissolved  gold  or  precious 
metal  out  of  its  cyanide  solution  by  means  of  aluminium  alloy  or  aluminium  amalgam- 
but  this  can  also  be  applied  with  advantage  to  sulphurized" solutions  containing  free 
alkali— that  is  to  say,  solutions  which  contain  gold  in  the  form  of  sulphuret,  or  hyposul- 
phide  of  gold. 

Zinc  has  heretofore  been  employed  in  practice  by  preference  in  precipitating  gold 
from  the  cyanide  solutions  obtained  by  leaching  auriferous  ores.  The  employment  of 
zinc  for  this  purpose  is  found,  however,  to  be  attended  with  serious  disadvantages.  Now 
I  have  discovered  that  aluminium  can  be  employed  for  this  purpose  in  place  of  zinc' 
without  the  disadvantages  attending  the  use  ot  the  latter.  ' 

Whilst  zinc  forms  a  combination  with  the  bound  or  free  compound  of  cyanogen  and 
alkali  contained  in  the  cyanide  solution,  aluminium  separates  the  gold  very  quicklv  from 
the  cyanogen  solution  without  entering  into  combination  with  the  cyanogen,  but  simplv 
reacting  with  the  caustic  alkali  which  is  present  at  the  same  time.  By  the  action  o"f 
aluminium  the  cyanide  of  potassium  employed  for  leaching  the  gold  out  of  its  ore  is 
regenerated,  which  is  not  the  case  when  zinc  is  employed.  But  the  zinc  does  not  con- 
fine itself  to  entering  into  combination  with  the  cyanogen  of  the  cyanogen  compounds 
of  the  gold,  but  also  acts  upon  the  free  cyanide  of  potassium  conta"ined  in  the  solution 
so  that  a  great  part  of  the  latter  is  consumed;  but  this  is  not  the  case  when  aluminium 
is  employed. 

These  results  are  of  the  greatest  importance  when  the  solutions  separated  from  the 
gold  is  to  be  employed  in  subsequent -gold-extracting  operations,  as  the  whole  of  the 
cyanogen  in  the  regenerated  and  liberated  cyanide  of  potassium  is  enabled  to  renew  its 
aetion;  but  the  lyes  resulting  from  the  employment  of  zinc  cannot  be  employed  with 


128  THE    CYANIDE    PROCESS. 

the  same  advantage  in  subsequent  operations  for  the  extraction  of  gold.  Numerous 
attempts  have  been  made  to  regenerate  the  zinc,  but  are  found  to  be  inconvenient  and 
costly.  It  is  consequently  evident  that  an  important  saving  in  cyanide  of  potassium  is 
obtained  by  the  employment  of  aluminium. 

Aluminium  acts  in  a  like  manner  in  a  sulphurized  alkaline  solution — that  is  to  say, 
in  a  solution  containing  the  gold  in  the  form  of  sulphuret  of  gold  or  hyposulphide  of 
gold.  It  does  not  enter  into  combination  with  the  sulphur  in  a  solution  of  this  descrip- 
tion. _  This  great  and  important  advantage  attending  to  the  employment  of  aluminium, 
aluminium  alloys,  or  aluminium  amalgam,  is  combined  with  other  advantages,  as  follows: 

Aluminium  is  far  less  subject  to  oxidation  than  is  zinc,  so  that  it  can  be  sent  from  its 
place  of  production  in  the  form  in  which  it  is  to  be  used  for  the  precipitation,  whereas 
when  zinc  is  employed  it  is  considered  to  be  an  important  advantage  to  reduce  it  to  the 
required  form  at  the  place  where  it  is  employed,  and  immediatelj'  before  using  it.  For 
the  same  reason,  the  repeated  employment  of  the  aluminium  is  admissible  for  con- 
tinuous precipitation. 

Finally,  the  quantity  of  aluminium  required  for  precipitating  the  same  quantity  of 
precious  metal  is  about  four  times  less  than  the  amount  of  zinc  required  to  produce  the 
same  effect. 

I  am  aware  that  attempts  have  been  made  to  employ  aluminium  for  precipitating 
precious  metals  from  acid  or  neutral  solutions,  but  in  this  case  it  offers  no  advantages 
as  compared  with  zinc  and  iron. 

On  the  other  hand,  the  practical  precipitation  of  precious  metals  from  alkaline 
cyanide  solutions  or  sulphurized  solutions  by  means  -of  aluminium  was  not  known, 
neither  was  it  known  that  by  the  employment  of  the  same  in  the  presence  of  free  alkali 
it  was  possible  to  obtain  the  important  advantages  hereinbefore  set  forth. 

Of  course,  instead  of  pure  aluminium,  alloys  or  an  amalgam  thereof  can  be  used  with 
a  like  advantage;  furthermore,  I  do  not  confine  myself  to  the  use  of  the  aluminium,  its 
alloys  or  amalgam,  in  any  special  form,  as  it  may  be  used  in  any  sxiitable  form  without 
departing  from  my  invention. 

Having  particularly  described  and  ascertained  the  nature  of  my  said  invention,  and 
in  what  manner  the  same  is  to  be  performed,  I  declare  that  what  I  claim  is — 

1.  Extracting  gold  and  other  precious  metals  from  their  ores  by  subjecting  the  ores  to 
the  dissolving  action  of  a  cyanide  of  an  alkali  or  an  alkaline  earth  in  the  presence  of  an 
oxidizing  agent,  substantially  as  and  for  the  purpose  hereinbefore  set  forth. 

2.  Extracting  gold  from  its  ores  by  subjecting  the  ores  first  to  the  action  of  an  acid 
and  subsequently  to  the  dissolving  action  of  cyanide  of  an  alkali  or  an  alkaline  earth  in 
the  presence  of  an  oxidizing  agent,  substantially  as  and  for  the  purpose  hereinbefore 
set  forth. 

3.  Extracting  gold  from  its  ores  by  subjecting  the  ores  to  the  dissolving  action  ol 
cyanide  of  an  alkali  or  an  alkaline  earth  in  a  ball-mill,  substantially  as  and  for  the  pur- 
pose hereinbefore  set  forth. 

4.  Precipitating  gold  or  other  precious  metals  out  of  their  solutions  by  means  of 
aluminium,  aluminium  alloys,  or  aluminium  amalgam,  in  the  presence  of  a  free  alkali, 
substantially  as  hereinbefore  described. 

Dated  August  31,  1893. 

CARL  MOLDENHAUBR. 


PATENT-SPECIFICATIONS.  129 

NEW   ZEALAND   PATENT   OFFICE. 


CARL  MARIA  PIELSTICKElf. 

APPLICATION  FOE  LETTERS   PATENT  FOR  IMPROVEMENTS  IN  THE  EXTRACTION  OF 
GOLD  AND  SILVER  FROM  ORES. 


I,  Carl  Maria  Pielsticker,  of  No.  43  Connaught  Road,  Harlesden,  in  the  county  of  Mid- 
dlesex, England,  engineer,  do  hereby  declare  the  nature  of  my  invention  for  Improve- 
ments in  the  Extraction  of  Gold  and  Silver  from  Ores,  and  in  what  manner  the  same  is 
to  be  performed,  to  be  particularly  described  and  ascertained  in  and  by  the  following 
statement : 

My  invention  has  for  its  object  the  extraction  of  gold  and  silver,  particularly  from 
sulphide,  and  from  such  ores  in  which  the  precious  metals  exist  in  a  state  of  extremely 
fine  division,  and  it  consists  essentially  in  treating  the  powdered  ore  with  a  solution  of 
cyanide  of  potassium  or  a  cyanide  or  cyanogen-yielding  substance  in  conjunction  with 
an  electric  current,  continuous  circulation  of  the  solvent,  continuous  precipitation  of 
the  dissolved  precious  metals  by  electrolysis,  and  continuous  regeneration  of  the  solvent. 

In  carrying  out  my  invention,  I  employ  a  tank,  marked  A  on  the  accompanying 
drawing,  which  I  call  the  ore-tank,  in  which  the  ore  is  subjected  to  the  treatment  with 
cyanide  of  potassium  in  conjunction  with  an  electric  current.  About  3  inches  from  the 
bottom  I  place  a  perforated  plate,  H,  preferably  of  iron  or  carbon,  covered  with  a  porous 
material,  such  as  cocoanut  matting.  The  plate  H  serves  as  anode,  and  is  insoluble,  or 
practically  so,  in  cyanide  of  potassium. 

If  made  of  iron,  I  prefer  a  highly  carburetted  iron,  or  ore  containing  a  high  percentage 
of  silicum.  Near  the  top  of  the  ore-tank  I  place  a  second  perforated  plate,  G,  which 
serves  as  cathode.  Both  these  plates  are  connected  by  means  of  insulated  wires,  e — e, 
with  a  dynamo,  D,  or  other  source  of  electricity. 

The  ore-tank  A  is  connected  near  its  top  by  means  of  a  pipe  with  a  second  tank,  B,  con- 
taining a  number  of  baffle  plates,  K,  or  their  equivalent,  which  are  destined  to  arrest  any 
suspended  matter  flowing  over  with  the  solution  from  the  ore-tank,  and  which  otherwise 
would  greatly  interfere  with  the  precipitation  of  the  dissolved  precious  metals  in  the 
following  tank,  C,  connected  with  the  tank  B  near  the  top  by  means  of  a  pipe.  The  pre- 
cipitating-tank  C  contains  one  or  more  pairs  of  electrodes,  M  and  N,  connected  with  the 
dynamo  D,  or  other  source  of  electricity,  by  means  of  the  insulated  wires,  g  and  gi,  of 
which  the  anode  preferably  consists  of  carbon  or  other  material,  insoluble,  or  practically 
so,  in  cyanide  of  potassium.  A  pump  P  is  connected  with  the  ore-tank  A  under  the 
anode  H  on  the  one  hand,  and  with  the  top  of  the  depositing-tank  C  on  the  other  hand, 
enabling  me  to  maintain  a  circulation  of  tne  solvent  througn  the  set  of  tanks. 

In  operating  my  invention,  I  fill  the  ore-tank  A  between  the  electrodes  H  and  G  with 
powdered  ore,  and  admit  into  the  three  tanks  A,  B,  and  C,  a  solution  of  cyanide  of 
potassium,  filling  them  above  the  level  of  the  pipes  which  connect  one  tank  with  the 
other.  The  strength  of  the  cyanide  solution  may  vary,  care  being  taken  to  have  suffi- 
cient cyanogen  present  to  bring  the  gold  and  silver  in  the  ore  into  the  solution,  the 
amount  of  which  has  previously  been  ascertained  by  assay.  I  connect  the  electrodes  H 
and  G  in  the  ore-tank  A,  and  ]M  and  N  in  the  depositing-tank  C,  with  the  dynamo  D,  or 
other  source  of  electricity,  and  force  the  cyanide  solution  from  below  through  the  ore  in 
the  tank  A. 

The  solution  pregnant  with  dissolved  precious  metals  overflows  into  the  settling-tank 
B,  where  it  clears  itself  from  suspended  matter,  and  becomes  thus  fit  to  part  with  the 
dissolved  precious  metals  on  overflowing  into  the  depositing-tank  C,  where  the  latter  are 
precipitated  on  the  cathode,  and  from  which  they  are  recovered  by  amalgamation  or 
otherwise.  The  cyanide  solution,  freed  from  dissolved  metals,  and  therefore  in  a  better 
condition  to  dissolve  more  metal  than  when  loaded  with  metal  in  solution,  is  pumped 
from  the  depositing-tank  C,  again  through  the  ore  in  the  tank  A,  where  it  dissolves  a 
fresh  proportion  of  precious  metals,  and  so  on,  continuously,  until  the  precious  metals 
contained  in  the  ore  under  treatment  are  dissolved. 

In  this  manner  my  process  becomes  a  continuous  one,  of  dissolving  the  precious  metals 
from  the  ore,  preparing  the  solution  pregnant  with  dissolved  metals  for  electrolysis  by 
separating  continuously  the  suspended  matter  therefrom,  precipitating  continuously 
the  dissolved  metals  by  electrolysis,  and  regenerating  continuously  the  solvent  for 
further  action  on  the  undissolved  precious  metals  still  contained  in  the  ore.  Very  little 
of  the  precious  metals  are  precipitated  on  the  cathode  G  in  the  ore  tank,  as  the  amount 
of  the  suspended  matter  present  in  the  solution  interferes  with  precipitation  in  this  tank. 

The  electric  current  in  the  depositing-tank  must  be  of  lo.w  tension,  and  so  regulated 
as  to  be  of  just  sufficient  strength  to  deposit  the  gold  and  silver  without  also  decompos- 
ing the  cyanide  of  potassium  ;  the  gold  and  silver,  being  more  readily  precipitated  from 
their  double  salts  of  cyanide  of  gold  (or  silver)  and  potassium  than  the  cyanogen,  is  set 
free  from  the  simple  salt  of  cyanide  of  potassium  so  long  as  the  current  of  electricity 
is  sufficiently  low  in  tension,  and  so  long  as  there  are  metals  present  in  the  solution. 

9cr 


130  THE   CYANIDE    PROCESS. 

The  original  solution  can  therefore  be  used  over  and  over  again  for  a  long  time,  and 
only  the  loss  made  good  occasionally. 

In  practice  I  find  that  an  electro-motive  force  of  about  one  volt,  and  an  intensitjr  of 
about  ten  amperes  per  square  meter  of  surface  of  cathode,  is  well  adapted  for  depositing 
the  gold  and  silver  in  the  tank  C.  I  may  find  it  desirable  to  employ  a  current  of  elec- 
tricity of  greater  potential  in  the  ore-tank  A  and  of  lesser  potential  in  the  depositing- 
tank  0. 

The  great  advantage  in  treating  ores  with  cyanide  of  potassium  in  conjunction  with 
an  electric  current  lies  in  the  fact  that  the  precious  metals  are  attacked  by  the  cyanide 
solution  more  energetically  in  conjunction  with  a  current  of  electricity  than  without 
one;  furthei,  when  the  dissolved  precious  metals  are  precipitated  by  means  of  an  elec- 
trical current  and  an  insoluble  anode  very  little  cyanide  and  no  metal  is  consumed,  as 
is  the  case  when,  for  instance,  zinc  is  used  as  a  precipitant,  when  not  only  zinc  is  con- 
sumed, but  also  cyanide  of  potassium  in  the  formation  of  a  double  salt  of  cyanide  of 
zinc  and  potassium.  Moreover,  serious  losses  in  gold  and  silver  are  occasioned  in  the 
recovery  of  the  precious  metals  from  the  zinc  slimes,  whereas  nothing  can  be  simpler 
than  their  recovery  from  the  cathode  by  amalgamation.  Again,  the  precipitation  of 
gold  and  silver  is  greatly  accelerated  by  the  electric  current. 

When  these  metals  are  precipitated  by  zinc  without  a  current  of  electricity,  the  latter 
goes  into  solution  as  a  double  salt  of  cyanide  of  zinc  and  potassium,  but  the  amount  of 
zinc  which  is  converted  into  cyanide  of  zinc  is  directly  proportionate  to  the  time  dur- 
ing which  it  is  in  contact  with  the  cyanide  solution.  Therefore,  the  more  time  is  con- 
sumed in  precipitating  the  gold  and  silver,  the  more  cyanide  and  the  more  zinc  will  be 
wasted. 

The  cyanide  process  is  most  advantageously  employed  on  ores  in  which  either  the 
gold  is  so  finelj'  divided  in  a  free  state  that  it  is  difficult  to  retain  it  by  older  methods,  or 
for  sulphide  ores.  Free  gold  is  certainly  more  quickly  dissolved  by  cyanide  of  potas- 
sium in  conjunction  with  an  electrical  current  than  without  one.  As  regards  pyritic 
ores,  if  they  are  simply  iron  pyrites,  as  they  are  in  a  great  number  of  cases,  a  cyanide  of 
potassium  solution,  whatever  its  strength  may  be,  has  as  little  action  on  them  when 
used  in  conjunction  with  an  electric  current  of  the  strength  I  use  as  without  one.  only 
the  gold  and  silver  in  the  ore  are  more  quickly  dissolved  in  conjunction  with  an  elec- 
trical current  than  without  one. 

If  the  ores  contain  sulphides,  oxides,  or  carbonates,  for  instance,  of  coppei  and  zinc, 
these  are  as  easily  dissolved  by  a  cyanide  of  potassium  solution,  whether  employed  by 
itself  or  in  conjunction  with  an  electric  current  such  as  1  use.  Such  ores,  however,  I 
prefer  to  treat  first  with,  say,  a  5  per  cent  sulphuric  acid  or  other  acid  solution  in  water, 
or  a  strong  solution  of  sulphurous  acid  in  water  in  sufficient  quantity  to  dissolve  such 
metals,  then  leach  with  water,  and  then  treat  with  the  cyanide  solution  in  conjunction 
with  the  electric  current. 

I  would  have  it  understood  that  I  do  not  limit  myself  to  the  precise  details  herein  set 
forth  and  illustrated  on  the  drawing— for  example,  the  number,  nature,  and  position  of 
electrodes,  of  the  sources  of  electricity,  and  of  the  number,  shape,  and  position  of  the 
tanks;  all  may  be  varied  while  retaining  the  construction  and  combinations  for  the 
proper  carrying  out  of  my  process  of  extraction  of  gold  and  silver  from  their  ores; 
further,  I  am  aware  that  cyanide  of  potassium  has  been  used  in  conjunction  with  an 
electric  current  for  like  purposes,  and  I  make  no  broad  claim  thereto. 

Having  now  particularly  described  and  ascertained  the  nature  of  my  said  invention, 
and  the  manner  in  which  the  same  is  to  be  performed,  I  declare  that  what  I  claim  is— 

1.  The  process  of  separating  gold  and  silver  from  their  ores,  which  consists  in  treating 
the  powdered  ore  with  a  solution  of  cyanide  of  potassium  in  conjunction  with  an  electric 
current,  depositing  the  precious  metals  constantly  by  means  of  a  current  of  electricity 
of  low  tension  and  electrodes,  of  which  the  positive  one  is  insoluble  in  cyanide  of  potas- 
sium, and  bringing  the  cyanide  of  potassium  solution  thus  freed  from  dissolved  metals 
constantly  again  into  contact  with  the  ore,  whereby  I  obtain  a  continuous  process  of 
extraction  and  precipitation,  all  substantially  as  herein  described. 

2.  In  the  process  of  separating  gold  and  silver  from  their  ores  by  means  of  a  solution 
of  cyanide  of  potassium  in  conjunction  with  an  electric  current,  bringing  the  cyanide  of 
potassium  solution  freed  from  dissolved  metals  continuouslj'^  into  contact  with  the  ore, 
substantially  as  described. 

3.  In  the  above-described  process  of  separating  gold  and  silver  from  ores  by  means  of 
a  solution  of  cyanide  of  potassium  in  conjunction  with  an  electric  current,  depositing 
the  dissolved  metals  by  means  of  electrodes  contained  in  depositing-tank  or  tanks, 
an  electric  current  being  passed  through  the  ore-tank  and  depositing-tank,  substantially 
as  set  forth. 

4.  In  the  above-described  process  of  separating  gold  and  silver  from  their  ores  by 
means  of  a  solution  of  cyanide  of  potassium  in  conjunction  with  an  electric  current, 
treating  the  ore  with  an  acid  in  combination  with  a  subsequent  treatment  of  cj'anide  of 
potassium  in  conjunction  with  an  electric  current  and  continuous  circulation  of  the 
solution,  substantially  as  described. 

5.  In  the  above-described  process  of  separating  gold  and  silver  from  their  ores  by 
means  of  a  solution  of  cyanide  of  potassium  in  coni unction  with  an  electric  current, 
subjecting  the  ore  and  solution  in  the  ore-tank  to  an  electric  current  of  greater  potential, 
and  depositing  the  dissolved  metal  in  a  depositing-tank  by  an  electric  current  of  lesser 
potential,  substantially  as  described. 


PATENT-SPECIFICATIONS. 


131 


132  THE   CYANIDE   PROCESS. 

6.  In  the  above-described  process  of  separating  gold  and  silver  from  their  ores  in  con- 
j  unction  with  an  electric  current,  the  use  of  a  current  of  electricity  of  sufficient  strength 
to  decompose  the  double  salt  of  cyanide  of  gold  or  silver  and  potassium  without  decom- 
posing the  cyanide  of  potassium  itself. 

7.  In  the  above-described  process  of  separating  the  gold  and  silver  from  their  ores  in 
conjunction  with  an  electric  current,  the  combination  of  an  ore-tank  with  a  settling- 
tank  and  a  depositing-tank,  substantially  as  described. 

CARL  PIELSTICKER. 
By  W.  H.  Quick,  His  Agent. 
Dated  this  14th  day  of  December,  1893. 


PATENT-SPECIFICATIONS.  133 

UNITED  STATES  PATENT  OFFICE. 


WILLIAM  DAVID  JOHNSTON,  of  San  Francisco,  California. 

METHOD  OF  ABSTRACTING  GOLD  AND  SILVER  FROM  THEIR   SOLUTIONS   IN   POTAS- 
SIUM CYANIDES. 


Specification  forming  part  of  Letters  Patent  No.  522,260,  dated  July  3,  1894. 
(Application  filed  November  20, 1893.    Serial  No.  491,473.    No  specimens.) 

To  all  whom  it  may  concern: 

Be  it  known  that  I,  William  David  Jolmston,  a  citizen  of  the  United  States,  residing 
in  the  City  and  County  of  San  Francisco,  State  of  California,  have  invented  an  Improve- 
ment in  Methods  of  Abstracting  Gold  and  Silver  from  their  Solutions  in  Potassium 
Cyanide ;  and  I  hereby  declare  the  following  to  be  a  full,  clear,  and  exact  description  of 
the  same : 

Heretofore  when  solutions  of  gold  and  silver  have  been  made  in  potassium  cyanide, 
the  metals  have  been  recovered  from  their  solution  by  the  use  of  zinc  in  various' forms. 

The  object  of  my  invention  is  to  recover  the  metals  in  a  shorter  time,  and  more  eco- 
nomically, by  the  use  of  pulverized  carbon,  preferably  in  the  form  of  charcoal. 

To  carry  my  invention  into  effect,  I  take  carbon  in  a  pulverized  form  as  above,  and 
place  it  upon  suitable  supports  so  as  to  form  it  into  filters,  through  a  series  of  which  the 
cyanide  liquid  is  caused  to  pass  successively,  leaving  the  metal  deposited  upon  the 
carbon.  The  gold  and  silver  are  then  recovered  from  the  carbon  by  carefully  burning 
the  carbon,  and  smelting  the  residue  with  the  usual  fluxes.  By  thus  employing  a  series 
of  filters  through  which  the  solution  is  passed  successively,  I  am  able  to  recover  upward 
of  95  per  cent  of  the  precious  metal  contained  in  the  solution. 

When  only  one  filter  is  employed,  only  about  one  fourth  of  the  gold  can  be  extracted. 

Having  thus  described  my  invention,  what  I  claim  as  new,  and  desire  to  secure  by 
Letters  Patent,  is — 

1.  The  process  of  abstracting  gold  and  silver  from  their  solution  in  potassium  cyanide, 
consisting  in  passing  the  liquid  through  a  series  of  carbon  filters  within  which  the  gold 
is  arrested,  suDstantially  as  described. 

2.  The  process  of  abstracting  gold  and  silver  from  their  solution  in  potassium  cyanide, 
consisting  in  passing  the  liquid  through  a  series  of  carbon  filters  within  which  the  gold 
is  arrested,  and  then  recovering  the  metal  by  burning  the  carbon  and  smelting  the 
residue  with  suitable  fluxes,  substantially  as  described. 

In  witness  whereof  I  have  hereunto  set  my  hand. 

WILLIAM  DAVID  JOHNSTON. 
Witnesses: 

S.  H.  NOUBSK. 
H.   F.   ASCHBCK. 


Note. — The  patents,  where  the  country  is  not  mentioned,  are  to  be 
understood  as  being  issued  in  Great  Britain. 


c 

California _ go 

Capacity,  daily,  of  South  African  plants  ..J "" 60 

Cape  Colony. _ V [."V.[  I  68 

Carbonate  of  ammonia  and  cyanide "  H 

Cement  tanks 22-61 


MONTHLY  ANALYSIS  OF  GOLD  PRODUCTION  IN  THE  WITWATERSRAND  DISTRICT— APRIL,  1894. 
Peepahid  bi  WITWATEKSKAND  CHAMBER  OF  MINES.    A.  K.  GoLDBms,  Secretary. 


,  City  and  Suburban 

.  Crown  Reef 

.  Durban  Roodeport 

.  Dashwood  Synaicate 

.  Ferreira 

.  Geldenhuis  Estate - 

I.  Geldenhuis  Main  Reef 

.  Ginsberg _ 

.  Glencairn 

:.  George  Goch  (amalgamated) . 

.  George  and  May. - 

.  Henry  Nourse -- 

I.  .Tohannesburg  Pioneer 

'.  jubifee  ."r;;;""."!'/';"."; 

.  Knight's  Tribute  Syndicate  . . 

.  Langlaagtc  Estate 

.  Idnglaagt«  Block  6 

.  Langlaagtc  Royal 

.  Langlaagtc  United 

.  Ltiipaarda  Vlei  Estate 

.  May  Consolidated 

.  May  I)eep  L/evel- 


32.  NewHeriot  ... 

33.  New  Primrose . 

34.  New  Chimes... 

35.  New  Aurora  Wi 

36.  New  Blue  Sky . 


.  Princess  Estate , 

.  Paarl  Central 

.  Paarl  Central  (tailings).. 

'.  Kandfontein  

.  Robinson -. 

.  Salisbury 


.  Treasury 
.  United  Mi 
.  Van  Ryn  Estate 


Reef  (Roodeport)  . 
Village  Main  Reef"!"'.'.* 


.  Worcester 

.  Wolhuter 

Vogelstruisfonteii 


Rand  Central  Ore  Rednc 

Rand  Central  Ore  Reduction  Co. . 

Robinson  Company 

Received  by  banks  from  other  sou: 


Totals 237,213    2,376 


799  10 
1,234  7 
2,212    16 


1,262  13 
1,120  6 
1,817    18 


26.81      3.72    111,716    14 


Value  of  Yield. 


9,770 
S,959 
24,756 
11,716 


14,300 
12,531 
2,863 


6,179 
3,760 
6.455 


2,918 
4.622 
8,187 


10,192 
19,205 
7,101 


6,045 
5,646 
10,319 
11,086 


MacArthur-F. . 


Chlorination  .. 


From  ConcentiatcB. 


Yield  of  Gold. 


Chlorination  . 


Value  of  Yield. 


3,380 
9,417 


-MacArthur-F. 
MacArthur-F. , 
MacArthur-F. . 
MacArthui^F. . 
MacArthur-F. , 
MacArthur-F. 


MacArthur-F. 
MacArthnr-F. 
MacAithur-F. 


MacArthur-F. . 


MacArthur-F. 
MacArthur-P. 
MacArthur-F. 
MacArthur-F. 
Mac.\rthur-F. 
MacArthur-F. 


MacArthur-F. 


MacArthur-P. . 
MacArthur-F. . 
MaoArthnr-F.  . 
MacArthur-F. . 
MacArthur-F. . 
MacArthur-F. . 


MacArthur.F. 
MacArthur-F. 
MacArthur-F. 
MacArthur-F. 
MacArthur-F. 


MacArthur-F. , 
MacArthur-F. . 
MacArthur-F. , 


MacArthur-P. . 
MacArthur-'F.". 


7,915 
1,300 
2,910 


6,651 
19,416 
1,320 


Yield  of  Gold. 


211,764    47,147        0      4.42 


Value  of  Yield. 


14,806 
6,337 
1,149 


1  2  10 
0  14  6 
0  13  11 
0  14    7 


1,049 
2,610 
14,088 


1,366 
4,205 
1,109 


0  16  1 
0  17  11 
0  10  8 
0  7  10 
0  10    2 


3,622  19 

3,507  4 

12,063  0 

6,344  12 


2,260  14 
13,003  U 
2,787    12 


241  19 

3,841  2 

6,803  0 

2,486  11 

1,719  0 

616  19 

1,479  17 

1,908  14 

1,122  0 

3,628  6 

3,034  6 

1,120  5 

2,581  10 

271  18 

3,630  14 

12,372  18 


3,019  0 

3,889  3 

2,377  17 

2,628  14 


18,063 
1,149 
17,630 


2,031 
12,961 
6,179 
3,750 


42,660 
9,455 
13,172 


10,862 
13,679 
8,620 
8,874 


Coucentrales  Produced 
During  the  Month,  f 


Value 
per  Ton, 


63.00  2.20 


10.00  4.00 


82.00 
94.00 
67.76 


J.  Falk,  tributor. 
25  per  cent  dividend. 


Concentrates  treated  by  Rand  Central  Ore  Reduction  Co. 

Milling  for  five  days  in  March  included. 

Tailings  sold  to  Rand  Central  Ore  Reduction  Co.   Concentrates  to  Robinson  Co. 


Tailings  treated  by  Lace  and  Thompson. 


Six  days'  milling  in  March  included. 

Concentrates  sold  to  Rand  Central  Ore  Reduction  Co. 


10  per  cent  dividend. 
Alluvial  from  5,304  loads. 


Where  the  value  of  the  gold  i 


In  calCQlfttiDg  the  total  averages,  allowance  is  made  for  defecti' 


10s.  per  oz.  for  mill  gold,  i 


ubllBbed  on  the  leBpoQaiblltty  of  the  companies  concerned. 


Prom  Mill 111,715 

Prom  Concentrates.  5,618 

From  Tailings 47,147 

From  Alluvial 142 

From  othersources.  4,121 

Totals 168,745 


£402,500 
21,476 
142,013 


INDEX. 


A 

Page. 

Absorption  of  cyanide  by  wood 28 

Accidents  in  cyanide  works... 45 

Acidity ; 45 

determination  of 44 

Advisability  of  tailings  concentration. 50 

Aeration  of  ore _.  50 

Africa _ 5-46 

African  Gold  Recovery  Company 46-55 

Agitation  and  filtration  by  tne  same  apparatus 21 

Agitation  process 20 

advantages  and  disadvantages 20 

time  of ^  20 

Agitator  at  Utica  Mine _  .  .  90 

of  steel .'. 20 

Alkali,  action  on  the  zinc 34-35 

Alum,  addition  of,  for  bullion  settling 34 

Aluminium  for  bullion  precipitation 40 

Amount  of  cyanide  solution  used  for  tailings 25 

Antidote  to  cyanide  poisoning 46 

Antimonial  ores  and  cyanide 15-16 

Antimony  in  zinc  bullion 35 

Arizona 87 

Arrangement  of  plants 55 

Arsenic  in  zinc  bullion _.  35 

Arsenides I5 

Australasia 69 

Australian  Gold  Recovery  Company _ gi 

Australian  ores,  cyanide  experiments  with n 

B 

Bagration,  Prince  Pierre 6  9 

Banket '"]  45 

Barrels  for  agitation 20 

Barrett  Company,  South  Africa 47-48 

Barry [."l'[l[[[]  71 

Bettel  process 52 

Black  Hills,  Gold  and  Silver  Mining  Company,  South  Dakota ..[-.-T. .'"!  87 

Bohm  process 76 

Borneo .'../..  95 

Bottom  discharge  for  tailings .1.'"..  59 

Bright  Star  Mine,  California .....  88 

Buckland,  J.  M. .........5-25-^6 

Bullion,  calcining  process  of 36-54 

fineness  of ........  55 

filter  in  Utica  Mine .....  92 

fluxes ........  37 

left  in  slag... 1.1^1.1.11!!.  54 

melting "l.."'..  37 

precipitation  in  Utica  Mine ...111.1111111  91 

precipitation  by,  zinc 111111111'  34 

precipitation  by  charcoal  1. 1. "Villi  40 

precipitation  by  lead 1!1.1111  33 

pulverizer , 1111!!        1  37 

refining  by  nitre 1!1!.!1111'!  54 

refining  by  sulphuric  acid .       '"'  36 

Butters,  Chas... 1111111!!!  118^55-59-63 

C 

California gg 

Capacity,  daily,  of  South  African  plants  ..."... ll!!!    60 

Cape  Colony lllllllllll! 68 

Carbonate  of  ammonia  and  cyanide l.llllll n 

Cement  tanks 111!!!! 22-61 


INDEX. 


A 

Page. 

Absorption  of  cyanide  by  wood 28 

Accidents  in  cyanide  works... 45 

Acidity ." 45 

determination  of 44 

Advisability  of  tailings  concentration... 50 

Aeration  of  ore 50 

Africa _ ..  5-46 

African  Gold  Recovery  Company 46-55 

Agitation  and  filtration  by  the  same  apparatus 21 

Agitation  process  _.. 20 

advantages  and  disadvantages 20 

time  of - .- 20 

Agitator  at  Utica  Mine.-- -  - .  .  90 

of  steel - ■. 20 

Alkali,  action  on  the  zinc _ 34-35 

Alum,  addition  of,  for  bullion  settling 34 

Aluminium  for  bullion  precipitation 40 

Amount  of  cyanide  solution  used  for  tailings 25 

Antidote  to  cyanide  poisoning 46 

Antimonial  ores  and  cyanide 15-16 

Antimony  in  zinc  bullion 35 

Arizona 87 

Arrangement  of  plants 55 

Arsenic  in  zinc  bullion 35 

Arsenides 15 

Australasia 69 

Australian  Gold  Recovery  Company 81 

Australian  ores,  cyanide  experiments  with 11 

B 

Bagration,  Prince  Pierre 6,9 

Banket 46 

Barrels  for  agitation 20 

Barrett  Company,  South  Africa 47^8 

Barry 71 

Bettel  process 52 

Black  Hills,  Gold  and  Silver  Mining  Company,  South  Dakota 87 

Bohm  process 76 

Borneo 95 

Bottom  discharge  for  tailings 59 

Bright  Star  Mine,  California _ 88 

Buckland,  J.  M ...5-35-46 

Bullion,  calcining  process  of 36-54 

fineness  of 55 

filter  in  Utica  Mine 92 

fluxes 37 

left  in  slag _ 54 

melting _._ 37 

precipitation  in  Utica  Mine 91 

precipitation  by,  zinc _ 34 

precipitation  by  charcoal 40 

precipitation  by  lead _  33 

pulverizer 37 

refining  by  nitre 54 

refining  by  sulphuric  acid 36 

Butters,  Chas i8^55-5&-<33 

C 

California 88 

Capacity,  daily,  of  South  African  plants  ...*... qq 

Cape  Colony 68 

Carbonate  of  ammonia  and  cyanide 11 

Cement  tanks 22-61 


136  INDEX. 

Page. 

Centrifugal  agitator  and  separator ., 21 

Champie's  mine,  Arizona 87 

Charter's  towers,  Queensland 81 

Chemistry  of  process .  6-16 

Childs^  I.  S 87 

Chronic  losses  of  bullion 42 

Circulating  system  in  Robinson  works 25 

Clark,  T.  C ...10-103 

Cleaning  up  of  bullion ..  34 

Clenell 18-55 

Coating  of  gold  ores 15 

iron  and  steel  vats  . 25 

wooden  vats    ...- 25 

Colorado ' 86 

Colombia,  Republic  of. 95 

Consumption  of  cyanide  in  Johannesburg 51 

Consumption  of  zinc  in  Johannesburg 53 

Con.  Virginia  and  California  Company _ 87 

Copper  compounds,  refractory 15 

cyanide,  consumption  by 16 

Copper  in  gold  precipitates 35 

Cost  of  cyanide  plants 43 

in  Johannesburg 55 

Cost  of  cyanide  treatment  in  Johannesburg 55 

Cost  of  Utica  plant    94 

Crawford,  J.  J.,  State  Mineralogist,  California 5 

Cripple  Creek  Gold  Extraction  and  Power  Company 86 

ores 87 

Cross  James.. 94 

Crown  mine  plant  of  Karangahake,  N.  Z. 69 

Crown  Reef  Company,  Johannesburg 55-60-62-65 

Croydon,  Queensland 81 

Custom  Mill,  Government,  Mt.  Torrens,  South  Australia 81 

Custom  works  in  Johannesburg 68 

Cyanide.. 28-30-51 

process 5 

application  of,  in  South  Africa 48 

poisoning,  treatment  of 46 

price  of.- 30 

returns  in  New  Zealand.. 70 

solutions  -. '.  28-50 

analysis  of 29-44 

determination  of  strength  required 44 

in  the  mortar  boxes 28-48 

strength  of.. 28 

volume  of 29-65 

D 

Danger  in  working  the  process 45 

De  Kaapsehe  District 47 

Deep  Down  Mine,  New  Mexico 87 

Demonstration  of  process 6-20 

Determination  of  gold  and  silver  in  cyanide  solution 44 

Difficulties  in  percolating  concentrates 28 

Discharge  of  residues 56-61 

Dividends,  list  of,  in  South  Africa 65 

Dixon,  J - 6,11 

Durban  Roodeport  Company's  works 65 

E 

Effect  of  cyanide  on  wooden  vats 28 

Electric  methods 38-40 

Molloy 38 

Pielsticker 40 

Siemens  &  Halske ' 38 

Electro-plating 9 

Elkington,  G.  R.  and  H 6-9 

Ellis,  C.J ....9-14-126 

Eisner,  L. <> 

Endlich,  F.  M :... 6-11 

Errors  in  the  estimate  of  extraction 53 

Exemplification  of  the  process 46 


INDEX.  137 

P 

»  Page. 

Faraday 6-9 

Faucett,  H.  W 10-104 

Feldtmann,  W.  R 55-58 

Ferreira  Company 62-65 

Ferricyanide  and  cyanide,  Moldenhauer  process 14 

Ferrocyanide  experiments &-11 

Ferrocyanide  for  extracting  gold  and  silver 9-11 

Filling" and  discharging  of  vats 26 

Filter 79 

Filter  presses 21 

Filter  presses  for  slime  treatment 52 

Filtration  by  centrifugal  force 21 

Financial  success  of  cyanide  process  in  South  Africa 60 

Fineness  of  bullion  in  Crown  Eeef  Company.. 55 

Nigel  Company 55 

Rooinson  Company 55 

Utica  Company 43 

Fineness  of  ore _ 22 

Fitness  of  ore  for  cyanide  treatment .; 96 

examination  for 44 

Fisher,  H.  T 88 

Forest,  R.W.  and  W. ...6-12-110-115 

G 

Generation  of  hydrogen  in  the  zinc  boxes. 34 

of  hydrocyanic  acid... 17 

Gernet,  A.  von _ 39 

Gmelin 35 

Gold  and  Silver  Extraction  Company  of  America,  Limited 84 

Gold  production  of  South  Africa ._ 67 

Gold  Run  Mine 88 

Gold  solutions,  treatment  of 30 

Golden  Reward  works 88 

Gordon,  H.  A. ..69-71-73 

Greighton  Mining  and  Milling  Company,  Georgia 88 

H 

Hagen 6-9 

Halske.    See  Siemens  &  Halske •. 38 

Hay  ward,  A 94 

Hauraki  gold  fields,  cyanide  plants  on  the 69 

Havilah,  Kern  County,  California 88 

Henderson  Mountain  Mining  Company,  Montana 85 

Henry  Nourse  Company,  JohannesDurg 62 

History  of  process. 6-9 

Hydraulic  slime  separator  at  Salisbury  works 49 

1 

Iconoclast  Mine,  Cal... 89 

Irvine,  W.  E 59 

J 

Janin,  A 6-14-125 

Janin,  Louis,  Jr 6-11-84 

Johannesburg  ores -. 46 

Johnston,  W.  D. 5^14-40 

E 

Kendall,  E.  D 14-117 

Kuaotunu  gold  field 76 

L 

Labor  in  cyanide  works 68 

Laboratory  work 44 

Lane,  C.  D 90 

Langlaagte  Estate  Company 22-60-63-65 

cement  tanks 22 

Royal  Gold  Mining  Company 63 

liebig's  method  of  testing  cyanide 29 


138  INDEX. 

Page. 

Lime  treatment,  preliminary  of  ore 18-50 

Loss  of  cyanide  by  absorption  in  vats  and  tanks 17-28 

by  action  of  carbonic  acid.  -. 17 

by  hydrolysis 17 

gold  in  Johannesburg 52 

zinc  by  galvanic  action ..- 32 

M 

MacArthur,  J.  S 5-12-110-112-115-126 

Machinery  and  appliances  .  - - 43 

McLaurin 17 

Mercur  Mining  and  Milling  Company,  Utah _ 84 

Mercury  in  zinc  boxes 35 

Merrill,  C.  W ..6-14-125 

Methods  of  operation    ...        20 

Meyer  and  Charlton  Company 62-65 

Mexico - 95 

Mineralogist,  California,  State 5 

Mitchell  Creek  Gold  Mine,  New  South  Wales 81 

Moldenhauer,  Carl 14-40-127 

Molloy,  B.  C -.6-13-38-118 

Molloy  process  for  bullion  precipitation ^..    ...        38 

Molloy  separator ...  13 

Montana 85 

Montgomery,  T.  C 13-121 

Moratock  Mine,  N.  C... 88 

Mortars  with  double  discharge 22 

Mt.  Morgan  Mine 15 

Muffle  furnace  for  bullion  refining 36 

Miihlenberger,  N.  H _ 6-11 

N 

Nevada --- - 87 

New  Golden  Mountain  Gold  Mining  Company,  Victoria. 83 

New  Mexico 87 

New  South  Wales .  81 

New  Zealand 69 

Nigel  Company ...49-53-55-63 

Nitre  for  bullion  refining  in  South  Africa. 54 

Number  of  plants  in  South  Africa , .  ...  48 

O 

Otis  crusher. 71 

Output,  total,  of  Rand  mines 65-66-87 

Oxygen,  action  of,  in  cyanide  treatment .  9 

P 
Patents 6 

Patent  royalty  in  New  Zealand .        80 

Paul,  A.  B 36-88 

Percentage  of  extraction 40-52 

in  South  Africa 41 

in  New  Zealand 41-79 

in  United  States  of  America 41 

Percolation  of  concentrates - .- 28 

ores  .._- .- 22 

tailings. _ --- .--        24 

process - - ....  20-22 

Pielsticker,  Carl  M - - ....14-40-129 

Plant  in  South  Denver 86 

Precipitation  of  bullion  by  aluminium 40 

by  charcoal 40 

by  electricity - 38-40 

by  zinc - - 34 

Preliminary  experiments .- 44 

Primrose  Company,  Johannesburg 65 

Profits  of  cyanide  treatment  in  South  Africa 65 

Puzzler  Gold  Mining  and  Milling  Company. 87 

Q 
Queensland ■ --- —        81 


INDEX.  139 

B 

Page. 

Radoe,  W.  A 53-55-60 

Rae,  Julio  H ...6-9-101 

Rand  Central  Ore  Reduction  Company 39-63 

Rate  of  gold  extraction  at  Utica  Mine 94 

Reactions,  secondary 17 

Recovery  of  bullion 30-53 

Recovery  ot  bullion  at  Nigel  Company 53 

Reese  Mill,  Cal 89 

Refractory  ores,  definition  ot ._  15 

Residues,  discharging  of,  by  running  cranes 26 

sluicing  out  of---     26 

Returns  per  ton  of  tailings  in  Johannesburg -. 66 

Revenue,  jNIontana --. .._ 85 

Revivification  of  cyanide 38 

Robinson  Company         _.. 25-55-60 

plant - 63 

Rolls  for  dry-crushing - _- 42 

Rose,  R.  ..- - _- - 71 

Rotary  distributor  for  mixing  coarse  and  fine  tailings - 49 

Russia - - - -.. 94 

S 

Salisbury  works,  Johannesburg 28-49 

Sanders,  I.  F ___ 106 

Scheidel,  Dr.  A ..- 3^7-33^77-78-89-92 

Scope  of  process 6-15 

Screens  for  dry  crushing 22 

Selection  of  site  for  plant - 43 

Shasta  Gold  Recovery  Company 88 

Sheba  Mine  -- - 47 

Side  discharge  of  tailings  .-- - 48 

Siemens  and  Kalske  process - 38 

Silver,  precipitation  by  zinc 92 

Simpson,  Jerome  W -.6^10-107 

Slimes,  deleterious  to  percolation - 52 

Smith,  Halford  G __ 65 

Soda  treatment  of  ore 18 

Sodium  amalgam  for  bullion  precipitation 38 

Solubility  of  gold  and  silver  in  cyanide 9 

South  America .-. _ _ 95 

South  Australia -_ 81 

South  Dakota 87 

Standard  Mine,  California .- _.  95 

Stebbins  and  Porter... _ 88 

Straits  settlements _,  95 

Strength  of  solution  in  Crown  Reef  works 61 

Strength  of  solutions  in  Johannesburg 50 

Strong  solution  leaching 50 

Sulphates  of  alumina,  action  of  on  cyanide 1.  18 

Sulphates  of  magnesia,  action  of  on  cyanide *  is 

Sulphides _ "  15 

Sulphuric  acid,  preliminary  treatment  by ig 

Summary  and  conclusions __ qq 

Sylvia  Mine,  Tararu,  New  Zealand _ ...16-35-41-79 

T 

Tailings  .. _ 24 

channel  formation  in  percolation - 24 

mechanical  difficulties  in  percolation "_  25 

shrinkage  in  vats "  25 

Tasmania ""  80 

Taylor,  James - - ^_  81 

Te  Komata  Mine - ..11"  76 

Tellurides "ll[""l[.  20 

Tellurides  in  Cripple  Greek - 1111  87 

Time  of  treatment-- 1.111  25 

Time  required  for  percolation  of  concentrates 1...  111111  28 

Total  production  by  cyanide  process ll_]  5 

Trap  doors  at  vats HH  26 

Treatment  of  gold  solutions —11.1111  30 

ore  and  tailings  pulp  direct  from  the  battery 111111  28 

precipitates  in  Johannesburg H  54 


140  INDEX. 

Page. 

Tryflnke  Company,  plant  of -  76 

Turner,  F.  B.  and  R.  B. 85 

Turner,  J.  K 86 

U 

United  States  oi  America _._ 83 

Utah 84 

Utica  Mining  Company,  Cal 7&-89 

V 

Vacuum  filter,  Scheidel's 21-79-90 

at  Utica  Mine — -.  90 

Value  of  cyanide  gold  in  South  Africa 60 

Rand  tailings 52 

Vats  of  brick  and  cement 22-28-48 

circular , 48 

false  bottoms  of --. - 23 

made  of  iron  or  steel. 22 

made  of  wood - - - - ---  22 

wooden,  MacArthur  construction 22 

size  of,  in  common  use « 22 

table  giving  dimensions  and  materials  of ..-•. 27 

Victoria -. .- - 83 

Virginia  Gold  Mining  Company,  South  Australia 81 

W 

Waihi  Company,  New  Zealand 69-71 

Waiorongomai  Mines - 76 

Watts,  W.L - 88 

Webber,  G.  E.,  Jr 51-53-55 

Western  Australia 8(' 

Witwatersrand  gold  fields 46 

custom  works 68 

Worcester  Works 39 

Working  costs  of  process 42 

in  Utica  cyanide  works,  California --- 93 

Wright,  Dr 6-9 

Z 

Zinc  amalgam  as  precipitant - ..-  34 

as  precipitant -- - 30 

box,  MacArthur's  description  of .-- .--  32 

boxes,  material  of --- —  32 

box,  Scheidel's  construction .♦ 32 

dust  as  precipitant - - - 34 

ferrocyanide  of -  35 

filter,  A.  B.  Paul's ..-- 36 

filters  of  earthenware  and  porcelain 35 

final  cleaning  up  of .- 34 

for  precipitation  of  bullion 53 

loss  of^  by  alkali 19-54 

precipitation  of  gold  and  silver,  theory  of -. 34 

preparation  of  filiform ---  33 

preparation  of  shavings 34 

quality  of,  used  for  precipitation 32 


THIS    BOOK    IS    DUE    ON    THE    LAST    DATE 
STAMPED  BELOW 


JUL 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN  THIS  BOOK 
ON  THE  DATE  DUE.  THE  PENALTY  WILL  INCREASE  TO 
50  CENTS  ON  THE  FOURTH  DAY  AND  TO  $1.00  ON  THE 
SEVENTH  DAY  OVERDUE. 


HU  ^^1981 

JUN  1 9  1981 

APR  0  3  1989 
JUNi^9 
JAN04199r 

NOV  28  1389:!t5 

RECEIVED 
M07  2  ^  1989 
PHSYSCIUBRARy 


APR  OLW^l 

RECaVEDj 

MftR2«  1991 


■fl 


Book  SIip-15H<-8,'57(,CS107s4)456 


16)^P>9? 


California.  Dept.  of 
natural  resources.  Di- 
vision of  mines. 

PHYSICAL 
SCIENCES 
LIBRARY 


Call  Number: 


TN21; 


A3 
no,  5 


Ttv2-4 
C3 

vno.  ^ 


UNIVERSITY  OF  CALlFO«« 
DAVIS 

164892 


